Packed food pasteurizing device and pasteurizing method

ABSTRACT

A prepackaged food sterilizing apparatus for sterilizing a prepackaged food P has a high frequency generator  71 . A high frequency is supplied from the high frequency generator  71  to the prepackaged food P to sterilize the prepackaged food P by dielectric heating. The apparatus includes a food loading container  2   x  constituted by a pair of opposing electrodes  20  consisting of a lower electrode  210  and an upper electrode  220  to which the high frequency is supplied and an annular insulator  23  interposed between the opposing electrode pair  20 . The food loading container  2   x  has at least one food loading chamber  21  in which the prepackaged food P is loaded with an inner shape thereof substantially equal to an outer shape of the prepackaged food P.

FIELD OF THE INVENTION

The present invention relates to a prepackaged food sterilizingapparatus and a sterilizing method for sterilizing a so-calledprepackaged food obtained by sealably packing various foods in apackaging container such as a plastic bag and a plastic tray byapplication of a high frequency.

BACKGROUND ART

So-called prepackaged foods are rapidly widespread such that variousfoods are sealably packed in a packaging container such as a plastic bagand a plastic tray, and it is true to say that such prepackaged foodscontribute to the food style of modem society to a great extent. It hasbeen a common practice to heat the prepackaged foods for sterilizationafter a food is sealed in a packaging container. A certain heatingprocess (heat maturation process) is also applied to a certain kind offood, combined with heat sterilization, to improve tastes and flavors ofthe food.

At a last stage of heat sterilization, boiling and steaming aregenerally performed. However, boiling and steaming require a long timefor processing, which lowers sterilization efficiency, and in addition,the flavors of the food may be degraded. The applicants of thisinvention have proposed a high frequency heating apparatus in whichplural prepackaged foods are loaded in a flat sealed container and ahigh frequency power is supplied to the container by way of opposingelectrodes in a pressurized state (Japanese Patent Application No. HEI7-329296).

In the above high frequency heating apparatus, inside the containerwhere the prepackaged food is loaded is brought to a sealed state by theopposing electrodes in contact with a peripheral portion of thecontainer. Accordingly, it is possible to heat the inside of the sealedcontainer (food loading chamber) at a temperature of 100° C. or higherto sterilize the food in a short time.

In the above high frequency heating apparatus, pressurizing means forpressurizing the inside of the container is necessary. Particularly,since plural prepackaged foods are loaded in the cylindrical shapecontainer in the above apparatus, large size pressurizing means isnecessary, which would raise the installation cost for the apparatus.Further, it is difficult to uniformly apply a high frequency to theplural prepackaged foods loaded in the container. Specifically, theheated temperature may vary depending on the loaded position of theprepackaged food which hinders uniform heating, and there may occur asituation that sterilization is not completed with respect to theprepackaged food that has been loaded at a lower temperature heatingposition. Incomplete sterilization eventually leads to non-sterilizationdue to growth of bacteria.

To enhance sterilizing ability, there is an idea of applying a highfrequency to a prepackaged food for a longer time. However, this idealeads to energy cost rise which is not desirable in the economicviewpoint. Further, a new problem may be raised that the flavor of theprepackaged food is degraded due to over heating.

There have been proposed various sterilizing apparatuses by microwaveradiation in which a prepackaged food is accommodated in a supporthousing member made of a synthetic resin having an inner configurationsubstantially equal to the outer shape of the prepackaged food (EuropeanPatent No. 0269073 (European Patent Application No. 8711732B.2),Japanese Examined Patent Publication No. HEI 7-51060, Japanese ExaminedPatent Publication No. HEI 7-114672, Japanese Utility Model RegistrarNo. 2539778, and Japanese Patent No. 2778165).

In view thereof, an object of this invention is to provide a prepackagedfood sterilizing apparatus and a sterilizing method that enables assuredsterilization to a prepackaged food while suppressing process cost forsterilization.

DISCLOSURE OF THE INVENTION

An aspect of this invention is directed to a prepackaged foodsterilizing apparatus provided with a high frequency generating sectionto supply a high frequency voltage in order to sterilize a prepackagedfood by dielectric heating. The apparatus is equipped with a foodloading container including a pair of opposing electrodes having a firstelectrode and a second electrode to which the high frequency is applied,and an annular frame interposed between the pair of first and secondelectrodes. The container has at least one food loading chamber forloading the prepackaged food therein. The food loading chamber has suchan inner shape as to substantially match an outer shape of theprepackaged food.

In this arrangement, the food loading chamber of the container definedby the opposing electrode pair and the annular frame is adapted forloading one prepackaged food. Unlike the conventional case where a largenumber of prepackaged foods are loaded in a food loading chamber of alarge capacity to sterilize the foods by dielectric heating using a pairof opposing electrodes which may result in a drawback that the heatedtemperature of the prepackaged foods varies depending on the loadedposition and the prepackaged foods with incomplete sterilization may bedischarged, according to the inventive apparatus, performing serialprocess such that a certain number of prepackaged foods are loaded inthe food loading chamber(s) one after another and taken out therefromsuccessively after dielectric heating enables reliable sterilizationonto the prepackaged foods.

Further, since the food loading chamber has such an inner shape as tosubstantially match the outer shape of the prepackaged food, expansionof the food due to dielectric heating is prevented by an inner wall ofthe food loading chamber which obstructs breaking of a bag/trayconstituting the container. This arrangement eliminates a necessity ofpressurizing the inside of the food loading chamber on a large scale, asperformed conventionally, with an attempt to prevent burst-out of thefood, thereby contributing to installation cost reduction.

As another aspect of this invention, the first electrode and the secondelectrode may be each formed with an opposing plane shaped into a flatsurface parallel to each other, and the annular frame may have such aninner shape as to substantially match a side surface of the prepackagedfood. Thereby, the construction of the container can be simplified.Further, at least one of the opposing planes of the first and secondelectrodes may be formed with a recess of an inner shape substantiallymatching the outer shape of the prepackaged food, and the annular framemay be so shaped as to come into contact with an outer surface of theprepackaged food. In this case, the container can contain various typesof prepackaged foods.

As a still another aspect of this invention, the annular frame mayinclude a plurality of annular frame segments (first and secondsegments) placed one over another, and each of the annular framesegments may have such an inner shape as to match the side surface ofthe prepackaged food. Thereby, two prepackaged foods can be loaded inthe container at once. The first and second annular frame segments maybe dividably or integrally constructed.

As a yet another aspect of this invention, the prepackaged foodsterilizing apparatus may further comprise a holding means operable tothe opposing electrode pair to hold the shape of the food loadingchamber. The holding means securely holds the closed state of the foodloading chamber even if the inside of the chamber is pressurized byheating to prevent burst-out of the food. The holding means may includea pressing means for pressing the first electrode against the secondelectrode. The pressing means may preferably include a cylinder device.

As a still another aspect of this invention, the holding means mayinclude an engaging means for restricting the first electrode away fromthe second electrode. Preferably, the engaging means may include anengaging portion and an operable tab to alter the position of theengaging portion between an engaged position of rendering the first andsecond electrodes in a pressingly held state and a release position ofreleasing the held state.

As a yet another aspect of this invention, the engaging means mayinclude a band member for fastening the first and second electrodes.

Preferably, the apparatus may further comprise a heating means topromote heating of the container. In this case, it is possible topreheat the container to a certain temperature prior to dielectricheating. Preheating of the container enables heating the food to beloaded or that has been loaded therein to a certain temperature, whichimproves dielectric heating efficiency. Further, the heating means maybe used during dielectric heating which contributes to uniform heating.

As a still another aspect of this invention, the apparatus may furthercomprise a cooling means for cooling the heated container. Thisarrangement enables rapid cooling of the heated and sterilizedprepackaged food. Thereby, suppressed is overheating of the prepackagedfood which consequently suppresses degraded flavors and tastes of thefood.

As a further aspect of this invention, the apparatus may furthercomprise a transport path for transporting the container and a highfrequency apply section provided on the way of the transport path toapply a high frequency from the high frequency generating section to thefirst and second electrodes with respect to at least one of thecontainers transported along the transport path.

Also, constituting the transport path by a conveyor belt thatcirculatively moves between a pair of rollers enables efficienttransport of the container along with the circulative movement of theconveyor belt.

As a yet another aspect of this invention, the apparatus may furthercomprise a prepackaged food loading mechanism provided upstream of thetransport path from the high frequency apply section for loading theprepackaged food into the container, and a prepackaged food take-outmechanism provided downstream of the transport path from the highfrequency apply section for taking out the prepackaged food from thecontainer. This arrangement enables automatic sterilization ofprepackaged food while facilitating handling operation.

This invention also provides a prepackaged food sterilizing method ofsterilizing a prepackaged food comprising the steps of: loading aprepackaged food in a food loading chamber of a food loading containerwith an inner shape thereof substantially equal to the shape of theprepackaged food, the food loading chamber defined by a pair of opposingelectrodes and a frame member composed of an insulating material forholding the electrode pair in a spaced relation; and applying a highfrequency from a high frequency generating section to the space definedby the opposing electrode pair while holding the prepackaged food in thefood loading chamber to sterilize the prepackaged food by dielectricheating.

The above sterilizing method may further comprise the step of applying ahigh frequency from the high frequency generating section to the firstand second electrodes with respect to at least one of the containerswhile circulatively moving the containers along a transport path.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially cutaway perspective view of a food sterilizingapparatus as a first embodiment according to this invention;

FIG. 2 is a partially cutaway perspective view of an example of anannular insulator 23;

FIGS. 3A and 3B are cross sections of the food sterilizing apparatus inFIG. 1, FIG. 3A showing a state that a container is opened, FIG. 3Bshowing a state that the container is closed;

FIG. 4 is a block diagram showing an example of a high frequencygenerating means used in the apparatus of this invention;

FIGS. 5A and 5B are diagrams showing an example of heat sterilization bythe first food sterilizing apparatus, FIG. 5A showing a sequence ofsterilization, FIG. 5B being a graph showing a relation between thetemperature of a prepackaged food in a sealed state in each process forsterilization and time when the prepackaged food is loaded in a foodloading container 2 x.

FIG. 6 is a schematic cross section of a food sterilizing apparatus as asecond embodiment according to this invention;

FIG. 7 is a schematic cross section of a food sterilizing apparatus as athird embodiment according to this invention;

FIG. 8 is a perspective view of an example of an automatic heatsterilizing facility in which a heat sterilizing process by a foodsterilizing apparatus as a fourth embodiment according to this inventionis applied;

FIG. 9 is a schematic cross section showing a food sterilizing apparatusas a fifth embodiment according to this invention;

FIG. 10 is a partially cutaway perspective view showing a foodsterilizing apparatus as a sixth embodiment according to this invention;

FIGS. 11A and 11B are cross sections of the food sterilizing apparatusshown in FIG. 10, FIG. 11A showing a state that a container is opened,and FIG. 11B showing a state that the container is closed;

FIGS. 12A and 12B are cross sections of a food sterilizing apparatus asa seventh embodiment according to this invention, FIG. 12A showing astate that an upper electrode is raised, and FIG. 12B showing a statethat the upper electrode is lowered;

FIG. 13 is a schematic cross section of a food sterilizing apparatus asan eighth embodiment according to this invention;

FIG. 14 is a schematic cross section of a food sterilizing apparatus asa ninth embodiment according to this invention;

FIG. 15 is a perspective view of a prepackaged food loading container asa first modification according to this invention showing a state that acover is opened;

FIG. 16 is a perspective view of the first modified prepackaged foodloading container showing a state that the cover is closed;

FIGS. 17A and 17B are cross sections taken along the line A—A in FIG.16, FIG. 17A showing a state that the cover is opened, FIG. 17B showinga state that the cover is closed;

FIG. 18 is a perspective view of a prepackaged food loading container asa second modification according to this invention showing a state that acover is opened;

FIG. 19 is a perspective view of the second modified prepackaged foodloading container showing a state that the cover is closed;

FIGS. 20A and 20B are cross sections taken along the line B—B in FIG.19, FIG. 20A showing a state that the cover is opened, FIG. 20B showinga state that the cover is closed;

FIG. 21 is a cross section showing essential parts of a prepackaged foodloading container as a third modification according to this invention;

FIG. 22 is a cross section showing essential parts of a prepackaged foodloading container as a fourth modification according to this invention;

FIG. 23 is a cross section showing essential parts of a prepackaged foodloading container as a fifth modification according to this invention;

FIG. 24 is a cross section showing essential parts of a prepackaged foodloading container as a sixth modification according to this invention;

FIG. 25 is a perspective view of a food sterilizing apparatus as a tenthembodiment using the first modified prepackaged food loading containeraccording to this invention;

FIG. 26 is a block diagram showing an example of a control system of thetenth food sterilizing apparatus;

FIGS. 27A and 27B are diagrams showing a sequence of heat sterilizationconducted by the tenth food sterilizing apparatus, FIG. 27A showing thesequence of steps, FIG. 27B being a graph showing a relation between thetemperature of the prepackaged food in each step from preheating tocooling and time;

FIG. 28 is a perspective view of a food sterilizing apparatus as aneleventh embodiment using the second modified prepackaged food loadingcontainer;

FIG. 29 is a partially cutaway perspective view showing an alteration ofthe eleventh food sterilizing apparatus;

FIG. 30 is a block diagram showing an example of the control system ofthe eleventh food sterilizing apparatus;

FIGS. 31A and 31B are diagrams showing a heat sterilizing processconducted by the eleventh food sterilizing apparatus, FIG. 31A showing asequence of steps, FIG. 31B being a graph showing a relation between thetemperature of the prepackaged food in each step from preheating tocooling and time;

FIG. 32 is a diagram showing an alteration of a high frequency powersupply system in the eleventh embodiment;

FIG. 33 is a perspective view of a prepackaged food loading container asa seventh modification according to this invention showing a state thata cover is opened;

FIG. 34 is a perspective view of the seventh modified prepackaged foodcontainer showing a state that the cover is closed;

FIG. 35 is a cross section taken along the line C—C in FIG. 34;

FIG. 36 is a cross-sectional side view showing a prepackaged foodloading container as an eighth modification according to this invention;

FIG. 37 is a cross section of the eighth modified prepackaged foodloading container taken along the line D—D in FIG. 36;

FIGS. 38A and 38B are diagrams of a prepackaged food loading containeras a ninth modification according to this invention, FIG. 38A being aplan view, FIG. 38B being a cross-sectional side view;

FIGS. 39A and 39B are diagrams of a prepackaged food loading containeras a tenth modification according to this invention, FIG. 39A being aplan view, FIG. 39B being a cross-sectional side view;

FIG. 40 is a plan view showing a food sterilizing apparatus as afourteenth embodiment according to this invention;

FIG. 41 is a diagram showing a prepackaged food loading container as aneleventh modification according to this invention; and

FIG. 42 is a diagram showing a prepackaged food loading container as atwelfth modification according to this invention.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a partially cutaway perspective view showing a firstembodiment of a food sterilizing apparatus according to this invention.FIG. 2 is a partially cutaway perspective view showing an example of anannular insulator (annular frame) 23. FIGS. 3A and 3B are cross sectionsof the food sterilizing apparatus in FIG. 1, FIG. 3A showing a statethat a container is opened, and FIG. 3B showing a state that thecontainer is closed. As shown in these drawings, the food sterilizingapparatus 101 includes a food loading container 2 x in which aprepackaged food P is accommodated, a control system 700 provided with ahigh frequency generator (high frequency power generator) 71 forapplying a high frequency to the prepackaged food P in the food loadingcontainer 2 x, and a temperature adjusting means 400 for adjusting thetemperature of the food loading container 2 x.

In this embodiment, the prepackaged food P is such that a certain kindof food is packed in a rectangular-shape tray in plan view, as shown inFIG. 2. The tray-type prepackaged food P is formed with an annular rimP2 projecting outward from an upper end portion thereof. After the foodis put in the tray, a synthetic resin sheet P3 is adhered to the annularrim P2 by, for instance, thermal fusion to sealably pack the food in thetray-type prepackaged food P.

The food loading container 2 x includes an opposing electrode pair 20consisting of a lower electrode 210 and an upper electrode 220 oppositethe lower electrode 210, each formed of a rectangular shape metallicplate in plan view, and an annular insulator 23 interposed between theopposing electrode pair 20. A food loading chamber 21 encased by theannular insulator 23 is defined on the upper electrode 220. One of theelectrodes 210, 220 corresponds to a first electrode, and the othercorresponds to a second electrode in this invention. The prepackagedfood P is accommodated in the food loading chamber 21, held by theopposing electrode pair 20, and heated by application of a highfrequency. A high frequency in the range of several KHz to severalhundreds MHz is usable in this invention. A high frequency in the rangeof 3 MHz to 300 MHz may be preferably used depending on the kind ofprepackaged food.

In this embodiment, the annular insulator 23 is made of apolytetrafluoroethylene excellent in heat resistance and durability. AnO-ring 24 made of a synthetic rubber is attached to upper and lowersurfaces of the annular insulator 23 at a widthwise center thereof tosecurely keep the sealed state of the food loading chamber 21 with theO-rings 24 pressingly held between the opposing electrode pair 20. Asfar as the sealability of the food loading chamber 21 is ensured byholding of the annular insulator 23 by the opposing electrode pair 20,the O-ring 24 may be omitted.

The annular insulator 23 has such a size as to make thethree-dimensional configuration of the food loading chamber 21 definedin the center of the food loading container 2 x substantially equal tothat of the tray-type prepackaged food P. In this arrangement, an outerside surface of the tray-type prepackaged food P is rendered into aclose contact with an inner side wall of the food loading chamber 21, asshown in FIG. 3, when the prepackaged food P is loaded in the annularinsulator 23 to prevent a thermal expansion of the tray-type prepackagedfood P in a transverse direction.

Upon loading of the prepackaged food P in the annular insulator 23 onthe lower electrode 210 as shown in FIG. 3A, the upper electrode 220 islowered to render a ceiling of the upper electrode 220 in pressingcontact with the synthetic resin sheet P3 of the prepackaged food P, asshown in FIG. 3B when the upper electrode 220 comes into contact withthe annular insulator 23. Thus, the prepackaged food P is held by theopposing electrode pair 20 at a certain pressure (e.g., 3 kg/cm²⁰, toprevent a thermal expansion of the prepackaged food P in a verticaldirection.

In this embodiment, a pressing means (holding means) 25 is provided onan upper side of the upper electrode 220 to press the upper electrode220 downward so as to secure the sealability of the food loading chamber21. Specfically, the pressing means 25 includes a hydraulic cylinder 26that is supportively held by an unillustrated support frame provided atthe upper side of the upper electrode 220 and a piston rod 27 eachprojecting downward from the hydraulic cylinder 26.

An insulator 28 is provided between the piston rod 27 and the upperelectrode 220 to connect the pressing means 25 and the upper electrode220 in a mutually and electrically insulated state. In this embodiment,the insulator 28 is, for instance, made of a polyacetal resin or asilicon resin.

The temperature adjusting means 400 includes a steam generator 410having a boiler and the like, a cooling water supply source 420 such aswaterworks, a lower electrode temperature adjusting pipe 430 embedded inthe lower electrode 210 in a winding manner, and an upper electrodetemperature adjusting pipe 440 embedded in the upper electrode 220 alsoin a winding manner.

The steam generator 410 has a steam supply main pipe 410 a for drawingout steam generated therefrom. The steam supply main pipe 410 a isbranched into two sub pipes 410 b at a downstream end thereof. Therespective sub pipes 410 b are connected to an upstream end of the pipes430, 440. Further, an upstream end of the cooling water supply main pipe420 is connected to the cooling water supply source 420, and the coolingwater supply main pipe 420 a is branched into two cooling water supplysub pipes 420 b at a downstream end thereof. Downstream ends of therespective sub pipes 420 b are connected to the pipes 430, 440. Aflexible tube made of a synthetic resin (not shown) is provided at anappropriate position on the way of the sub pipes 410 b, 420 b toinsulate an upstream portion thereof from the opposing electrode pair20.

A control valve 450 is provided on the steam supply main pipe 410 a, anda control valve 460 is provided on the main pipe 420. Opening andclosing the control valves 450, 460 switchingly supplies steam from thesteam generator 410 and cooling water from the supply source 420 to thepipes 430, 440 to adjust the temperature of the container 2 x andconsequently the temperature of the prepackaged food P loaded in thechamber 21.

A downstream end of the pipes 430, 440 is formed into an open endopening outward. Steam and cooling water supplied through the pipes 430,440 are drawn out of the pipe system through the open end afteradjusting the temperature of the container 2 x.

An inner wall of the pipes 430, 440 is covered with an insulator toprevent the water and steam passing through the pipes 430, 440 frombeing adversely affected electrically.

FIG. 4 is a block diagram showing an example of the high frequencygenerating means according to this invention. As shown in FIG. 4, thecontrol system 700 includes a control means 710 for centrallycontrolling the food sterilizing apparatus 101, an operating unit 120for inputting various operation data to the control means 710, and thehigh frequency generator 71 for supplying a high frequency to the pairof opposing electrodes 20.

The control means 710 controls power supply to the high frequencygenerator 71 based on operation data inputted by way of the operatingunit 120. The operating unit 120 has an operation button section 123provided with a start-up button 121, a stop button 122, etc., as well asa data enter key 124 for inputting data such as the kind and weight ofthe prepackaged food P.

An operation signal from the start-up button 121 and the stop button 122is outputted to the control means 710 as a control signal via thecontrol means 710. When the start-up button 121 is operated, driving ofthe high frequency generator 71 starts, and when the stop button 122 isoperated, the driving thereof is suspended.

The high frequency generator 71 includes a power circuit 71 a, a highfrequency generating circuit 71 b for generating a high frequency uponpower supply from the power circuit 71 a, and a rectifying circuit 71 cprovided downstream of the high frequency generating circuit 71 b. Thepower circuit 71 a is for transforming a power of e.g., 220V forcommercial use to a direct current power of a predetermined level. Thecircuit 71 b is of a self-oscillating type which generates a highfrequency energy of a desired level upon supply of a DC voltage of thepredetermined level from the power circuit 71 a. The circuit 71 b may beof an enforced oscillating type. The rectifying circuit 71 c is acircuit for rectifying a current balance between the high frequencygenerating circuit 71 b and a current passing through a load(prepackaged food P) disposed between the opposing electrode pair 20,and includes a transformer 71 d and an unillustrated capacitor forrectification. A coil, or a capacitor and a coil may be used forrectification, in place of the capacitor.

The control means 710 enables to set a desired power supply level thatis obtained in advance based on experiments conducted under variousconditions of differentiated kind, volume and thickness of theprepackaged food P. Setting of the power supply level is executed byoperating the data enter key 124. Upon actuation of the data enter key124, an output power from the power circuit 71 a is set based on acomputation program stored in advance.

FIGS. 5A and 5B are diagrams showing an example of heat sterilization bythe first food sterilizing apparatus. FIG. 5A shows a sequence of heatsterilization, and FIG. 5B is a graph showing a relation between thetemperature of the sealed prepackaged food in each step forsterilization and time when the prepackaged food P is loaded in the foodloading container 2 x. As shown in FIG. 5A, the process of dielectricheat sterilization includes a loading step X1 where the prepackaged foodP is loaded in the food loading chamber 21 of the food loading container2 x, a sterilizing step X2 where the prepackaged food P loaded in thechamber 21 is heated for sterilization, a take-out step X3 where theprepackaged food P completed with the heat sterilization in thesterilizing step X2 is taken out, and a secondary cooling step X4 wherethe taken out prepackaged food P is immersed in cooling water filled inan unillustrated water bath for cooling the prepackaged food P.

In the sterilizing step X2, a temperature raising step X21 where thetemperature of the prepackaged food P is raised up to a sterilizingtemperature of 100° C. or higher (e.g., in the range from 110° C. to140° C.), a heating step X22 where the sterilizing temperature of theprepackaged food P obtained by the temperature raising step X21 isretained for a predetermined time to perform heat sterilization as wellas heat maturation, and a primary cooling step X23 where the temperatureof the prepackaged food P after retained for the predetermined time forheat sterilization is lowered to a substantially ambient temperature(temperature before the heating step X22) are performed sequentially.After the temperature of the prepackaged food P is lowered to a certaintemperature (lowest point: 100° C.) in the primary cooling step X23, asshown in FIG. 4B, the prepackaged food P is immersed in cooling waterfilled in the unillustrated water bath in the secondary cooling step X4after the take-out step X3 to lower the temperature thereof to anambient temperature. In the case where the package of the prepackagedfood P has a certain durability and there is no possibility of breakingthe package even if the inner pressure of the prepackaged food P exceedsslightly over 1 atm (for instance, around 1.1 atm), as shown by thedotted line in the graph of FIG. 4B, it may be possible to execute thetake-out step X3 before the temperature of the prepackaged food P lowersto 100° C. and then proceed to the secondary cooling step X4.

In the loading step X1, the prepackaged food P is loaded in the foodloading chamber 21 on the lower electrode 210. Thereafter, driving thehydraulic cylinder 26 in such a manner as to lower the piston rod 27lowers the upper electrode 220 downward to close a top opening of thefood loading chamber 21.

When the top opening of the food loading chamber 21 is closed, as shownin FIGS. 1 and 3B, the ceiling of the upper electrode 220 is pressedagainst the upper side of the annular insulator 23 to securely hold theloading chamber 21 in a sealed state. In this state, the top and bottomside of the prepackaged food P loaded in the food loading chamber 21respectively come into contact with the ceiling of the upper electrode220 and the bottom of the lower electrode 210 in a state that the outerside surface of the prepackaged food P comes into close contact with theinner side wall of the annular insulator 23. In the loading step X1, thecontrol valve 450 is kept in an opened state to continue heating thefood loading container 2 x by the steam supplied from the steamgenerator 410.

Next, the sterilizing step X2 is executed. In the sterilizing step X2, ahigh frequency starts to be supplied from the high frequency generator71 to the opposing electrode pair 20. Upon application of the highfrequency to the opposing electrode pair 20, the prepackaged food Ploaded in the food loading chamber 21 is subject to dielectric heating,and the temperature raising step X21 where the temperature of theprepackaged food P is raised to a predetermined temperature is executed.

In the temperature raising step X21, the temperature of the prepackagedfood P is, as shown in FIG. 5B, raised rapidly by dielectric heating.When the temperature of the prepackaged food P exceeds 100° C., watercontained in the food packed in the tray vaporizes, which may lead tothermal expansion of the prepackaged food P. At this time, the expansionof the prepackaged food P is prevented due to close contact of theprepackaged food P with the inner circumferential side of the annularinsulator 23 and the opposing electrode pair 20. Accordingly, the insideof the prepackaged food P is kept in a high-pressurized state whichraises the boiling point of water. Then, water inside the prepackagedfood P does not vaporize and stays as a liquid phase. When thetemperature of the prepackaged food P reaches the predeterminedtemperature (e.g., in the range from 110 to 140° C.), the driving of thehigh frequency generator 71 is suspended, and the sequence proceeds tothe heating step X22.

In the heating step X22, the temperature of the prepackaged food P iskept at the predetermined temperature (110 to 140° C.) for apredetermined time simply by steam supply from the steam generator 410to substantially effect a heat sterilization process to the prepackagedfood P by maintaining the temperature for the predetermined time. Uponcompletion of heat sterilization in the heating step X22, the primarycooling step X23 is executed.

In the primary cooling step X23, the control valve 450 is closed to stopsupply of steam from the steam generator 410 to the food loadingcontainer 2 x. Then, the control valve 460 is opened to supply coolingwater from the supply source 420 to the pipes 430, 440. Thereby, asshown in FIG. 5B, the temperature of the prepackaged food P in the foodloading chamber 21 is lowered down to the temperature at 100° C. orbelow. This cooling operation prevents long stay of the food at such atemperature that may cause growth of bacteria. This is effective inpreventing re-growth of bacteria in the prepackaged food P.

After the temperature of the prepackaged food P is lowered to 100° C. orbelow in the primary cooling step X23, then, in the take-out step X3,the upper electrode 220 is raised followed by lifting up of the pistonrod 27 by activation of the hydraulic cylinder 26 to open up the foodloading chamber 21. Then, the prepackaged food P is taken out from thefood loading chamber 21, put in the secondary cooling step X4 where theprepackaged food P is immersed in cooling water filled in theunillustrated water bath to lower the temperature thereof to an ambienttemperature. The above-mentioned each step in accordance with batchprocessing is cyclically repeated in the food sterilizing apparatus 101to sequentially perform heat sterilization to the prepackaged foods P.

In this invention, the prepackaged food P comes into contact with theinner wall of the food loading chamber 21 (namely, the inner side wallof the annular insulator 23 and the surface of the opposing electrodepair 20 in contact with the prepackaged food P). The inner wall of thefood loading chamber 21 enables preventing the prepackaged food P fromexpanding due to heat application, and thus reliably preventingburst-out of the tray-type prepackaged food P which may be caused byexpansion of the tray in the sterilizing step X2. Thus, the heatsterilization of the prepackaged food P at 100° C. or higher is securelyperformed, as well as carrying out heat maturation of the food toimprove flavors and tastes of the food.

Also, even if the temperature of the prepackaged food P is raised over100° C. in the sterilizing step X2, water contained in the food does notvaporize and stays as a liquid phase. In addition, the high-pressurizedstate quickly spreads inside the prepackaged food P to keep the innerpressure of the prepackaged food P at a constant value. In the course ofsetting the inner pressure of the prepackaged food P at the constantvalue, heat also propagates uniformly to set the temperature inside theprepackaged food P at a constant value in a short time. Thereby,variation of the heat sterilization over the entirety of the prepackagedfood P is avoided.

FIG. 6 is a schematic cross section showing a second embodiment of afood sterilizing apparatus 102 according to this invention, and FIG. 7is a cross section showing a third embodiment of a food sterilizingapparatus 103 according to this invention.

The food sterilizing apparatus 102 as the second embodiment is, as shownin FIG. 6, for sterilizing a tray-type prepackaged food P similar to thefirst embodiment. A lower electrode 210 a and an upper electrode 220 aconstituting an opposing electrode pair 20 a are formed with arecess/projection, in place of a flat surface, having such a shape as tomatch the configuration of a food loading chamber 21 and prepackagedfood P.

Specfically, the upper electrode 220 a is formed with a projection 221projecting downward at a center on a bottom surface thereof, and thelower electrode 210 a is formed with a housing recess 211 on a topsurface thereof at a position corresponding to the projection 221 with asurface area larger than the projection 221. A bottom surface of theprojection 221 is formed into a flat shape, and the housing recess 211has such a dimension as to match the configuration of the bottom sideand outer circumferential surface of the prepackaged food P.

An annular insulator (annular frame) 231 having a thickness (height)equal to the height of the projection 221 is mounted outside slidinglyalong an outer circumference of the projection 221 to set a bottom sidethereof flush with the bottom surface of the upper electrode 220 a. Inthis arrangement, when the upper electrode 220 a is placed over thelower electrode 210 a, a top surface of the lower electrode 210 a comesinto contact with the bottom side of the annular insulator 231 to makethe lower electrode 210 a and the upper electrode 220 a mutuallyinsulated from each other. At this time, the projection 221 and thehousing recess 211 define the food loading chamber 21 for accommodatingthe prepackaged food P therein. The other arrangement of the secondembodiment is the same as the first embodiment.

According to the food sterilizing apparatus 102 of the secondembodiment, an inner wall of the food loading chamber 21 is formedintegral with the metallic lower electrode 210 a to make the foodloading chamber 21 resistible against a higher pressure.

A prepackaged food loading container 20 b in the third embodiment is, asshown in FIG. 7, for sterilizing a prepackaged food PlO packed in a bag.In the third embodiment, whereas an upper electrode 220 b and an annularinsulator 231 have the same arrangement as the embodiment in FIG. 6, alower electrode 210 b has an ellipse shape in side view, and is formedwith a housing recess 212 having a configuration substantially identicalto the outer shape of the bag-type prepackaged food P10. The lowerelectrode 210 b has a two-pieces-make-one-unit arrangement in whichhalved left and right two pieces are joined together transversely tomake a whole one unit. Placing the bag-type prepackaged food P10 on thelower electrode 210 b in a state that the halved pieces are disposedapart and joining the pieces together enables fittingly accommodatingthe prepackaged food P inside the food loading chamber 21. The otherarrangement of the third embodiment is the same as the secondembodiment.

According to the food sterilizing apparatus 103 of the third embodiment,when the bag-type prepackaged food P10 is loaded in the food loadingchamber 21, the outer surface thereof fittingly comes into contact withthe inner wall of the food loading chamber 21 to prevent the bag-typeprepackaged food P10 from being burst out with the bag tom out duringthe heat-sterilizing process.

The food loading container 20 b in FIG. 7 is described as an example ofcontainer in the third embodiment. As an alternative, a pair of heattransmission plates 990 (shown by the block of imaginary line in FIG. 7)may be provided to hold the food loading chamber 20 b therebetween. Inthis case, forming a passage for passing a fluid (heating medium orcooling medium) in the pair of heat transmission plates 990 desirablyheats or cools the inside of the prepackaged food P10 from outwardthrough the food loading container 20 b. Altematively, a heatingconductor such as a nichrome wire may be embedded in the heattransmission plates 990 to heat the plates 990 by heat emission of theheating conductor.

Alternatively, it may be possible to make the configuration of the upperelectrode and lower electrode opposite in the arrangement of the foodsterilizing apparatus 102 of the second embodiment and the foodsterilizing apparatus 103 of the third embodiment.

FIG. 8 is a perspective view of an example of an automatic heatsterilizing facility in which a heat sterilizing process of a fourthembodiment of the food sterilizing apparatus according to this inventionis applied. As shown in FIG. 8, the automatic heat sterilizing facility55 includes a food sterilizing apparatus 104, a container feed mechanism56 provided upstream (left side in FIG. 8) of the apparatus 104, and acontainer discharge mechanism 59 provided downstream of the apparatus104.

In this embodiment, an annular insulator 23 itself functions as acontainer for loading and transporting a prepackaged food P downstream.Accordingly, the annular insulator 23 is hereinafter referred to as a“transportable container 23 a” in this embodiment. Prepackaged foods Pare successively loaded in a corresponding one of the food loadingchambers 21 of the transportable containers 23 a and transported to theapparatus 104 by way of the container feed mechanism 56. After appliedwith a certain heat sterilization by the apparatus 104, the prepackagedfoods P are successively fed to a next step by the container dischargemechanism 59.

The food sterilizing apparatus 104 is, in this embodiment, provided withan opposing electrode pair 20 a consisting of a lower electrode 210 aand an upper electrode 220 a, having a larger size than the opposingelectrode pair 20 in the aforementioned embodiments. In thisarrangement, three transportable containers 23 a are loadable on thelower electrode 210 a serially in a row as a group, and a top opening ofthese three transportable containers 23 a is altogether covered by theupper electrode 220 a. The other arrangement of the opposing electrodepair 20 a is the same as the first or second embodiment.

The container feed mechanism 56 includes a belt conveyor 57 for feedinga group of transportable containers 23 a from a preceding process to aheat sterilizing process, and a setting table 58 provided upstream ofthe apparatus 104 in parallel with the belt conveyor 57 for setting thegroup of containers 23 a in a line-up state prior to transport to theheat sterilizing process.

The belt conveyor 57, the setting table 58, and the lower electrode 210a are provided in such a height level as to set placing planes of therespective members for placing the transportable containers 23 a at thesubstantially same height level with each other. In this arrangement, agroup of containers 23 a are slidably conveyed from the placing plane ofthe belt conveyor 57 to the setting table 58, and then from the placingplane of the setting table 58 to the lower electrode 210 a.

A first pusher 57 a for pushing the group of containers 23 a from thebelt conveyor 57 onto the setting table 58 is provided on a lateral sideof the belt conveyor 57 opposite the setting table 58. A second pusher58 a for pushing the containers 23 a from the setting table 58 onto thelower electrode 210 a is provided on the setting table 58. The first andsecond pushers 57 a, 58 a reciprocate by driving an unillustrateddriving means such as a hydraulic cylinder.

The container discharge mechanism 59 includes a base block 590 providedadjacent the lower electrode 210 a downstream of the opposing electrodepair 20 a, and a roller conveyor 591 provided on an upper surface of thebase block 590. The roller conveyor 591 includes plural rollers, andeach of the rollers is rotatable about an axis normal to the transportdirection of the container 23 a. Driving each roller of the rollerconveyer 591 in the same rotating direction enables transport of thecontainers 23 a from the apparatus 104 to a next process.

The belt conveyor 57 is intermittently driven in such a manner that thedriving means is operated to forward a group of transportable containers23 a by a distance corresponding to the containers 23 a and then thedriving thereof is temporarily suspended. During the driving suspendstate of the belt conveyor 57, the first pusher 57 a reciprocates tomove the group of containers 23 a onto the setting table 58.

Then, the group of containers 23 a placed on the setting table 58 aretransported onto the lower electrode 210 a by driving the second pusher58 a in the transport direction of the containers 23 a. Aftertransported onto the lower electrode 210 a, the group of containers 23 aare altogether pressingly held between the upper and lower electrodes220 a, 210 a by lowering of the upper electrode 220 a. Then, the heatsterilizing process described with reference to FIG. 5 is performed ontothe prepackaged foods P respectively loaded in the transportablecontainers 23 a.

After completion of the heat sterilizing process by the apparatus 104,the upper electrode 220 a is lifted up, and then driving the secondpusher 58 a forward enables transport of the group of containers 23 aplaced on the lower electrode 210 a onto the roller conveyor 591.Driving the roller conveyor 591 upon landing of the containers 23 athereon enables feeding the same forward to the next process.

In this way, by driving the belt conveyor 57, first pusher 57 a, secondpusher 58 a and upper electrode 220 a intermittently in mutuallyassociated manner, the prepackaged foods P loaded in the group ofcontainers 23 a that have reached the belt conveyor 57 one after anotherare simultaneously applied with heat sterilization by the apparatus 104and discharged out of the apparatus 104 by the container dischargemechanism 59. This sequence is performed cyclically.

As shown by the solid black arrows in FIG. 8, a heating medium is drawninto the lower electrode 210 a and the upper electrode 220 a, and asshown by the blank arrows, the heating medium is drawn out therefrom. Inthis arrangement, the electrodes 210 a, 220 a are heated to promoteheating the inside of the prepackaged food P in addition to dielectricheating, thereby accelerating the sterilization by the apparatus. As analternative, introducing a heating medium into the electrodes 210 a, 220a during the dielectric heating and then introducing a cooling mediumupon completion of the dielectric heating makes it possible to rapidlycool the prepackaged food P completed with the sterilization. This iseffective in avoiding a situation that a certain temperature state,which may cause growth of bacteria, is continued for a long time.

Alternatively, the upper electrode 220 a may be divided into threesections as shown by the imaginary lines in FIG. 8, and compact highfrequency generators may be provided individually to the sections tosupply a high frequency power to each section. This arrangement makes itpossible to uniformly supply a high frequency power to the group offoods P between the opposing electrode pair 20 a.

According to the above automatic heat sterilizing facility 55, a greatnumber of prepackaged foods P can be subject to heat sterilizationwithout manpower, which is effective in suppressing operating cost ofthe food sterilizing apparatus.

FIG. 9 is a schematic cross section of a food sterilizing apparatus as afifth embodiment according to this invention. In this embodiment, thearrangement of a sealing member 23 is the same as the foregoingembodiments, except that an opposing electrode pair 20 b (lowerelectrode 210 b and upper electrode 220 b) is formed with a recess 210 cat a center thereof in opposing surfaces to fittingly receive upper andlower parts of a prepackaged food P packed in a cup-shape vessel. Theother arrangement of the fifth embodiment is the same as the firstembodiment.

FIG. 10 is a partially cutaway perspective view of a food sterilizingapparatus as a sixth embodiment according to this invention, and FIGS.11A and 11B are cross sections of the food sterilizing apparatus in FIG.10, FIG. 11A showing a state that a container is opened, and FIG. 11Bshowing a state that the container is closed. As shown in thesedrawings, the apparatus 106 includes a food loading container 2 y forhousing a prepackaged food Pa, a high frequency generating means 3 forapplying a high frequency to the prepackaged food Pa loaded in thecontainer 2 y, a heating medium supply means 470 for supplying heatedair as a heating medium and cooling water as a cooling medium into thecontainer 2 y, and a temperature adjusting means 400 for adjusting thetemperature of the container 2 y. Although the heating medium may besteam, heated air is used as the heating medium in this embodiment.

The food loading container 2 y includes, in this embodiment, an opposingelectrode pair 20 each made of a metallic plate member with arectangular shape in plan view and consisting of a lower electrode 210and an upper electrode 220 opposing the lower electrode 210, and anannular sealing member 23 x (corresponding to the annular insulator 23shown in FIGS. 1 to 9) provided between the opposing electrode pair 20along a perimeter thereof. A food loading chamber 21 encased by thesealing member 23 x is defined on the upper electrode 220. The dimensionof the sealing member 23 x is set such that the height thereof isslightly smaller than the thickness of the prepackaged food P and thecontent volume thereof is slightly larger than the volume of theprepackaged food Pa The prepackaged food Pa is accommodated in thechamber 21, held by the opposing electrode pair 20, and heated byapplication of a high frequency. A high frequency in the range ofseveral KHz to several hundreds MHz is usable in this invention. A highfrequency in the range of 3 MHz to 300 MHz may be preferably used inthis embodiment.

In this embodiment, the sealing member 23 x is made of apolytetrafluoroethylene excellent in heat resistance and durability. AnO-ring 24 made of a synthetic rubber is attached to upper and lowersurfaces of the sealing member 23 x at a widthwise center thereof tosecurely keep the sealed state of the food loading chamber 21 with theO-rings 24 pressingly held between the opposing electrode pair 20.

The thickness (height) of the sealing member 23 x is set in such amanner that an upper surface of the prepackaged food Pa comes intocontact with a ceiling of the upper electrode 220, as shown in FIG. 11B,with the upper electrode 220 in contact state with the sealing member 23x when the upper electrode 220 is lowered after loading of theprepackaged food Pa in the sealing member 23 x as shown in FIG. 11A

In this embodiment, a pressing means (holding means) 25 is provided onan upper side of the upper electrode 20 to press the upper electrode 220downward so as to secure the sealability of the food loading chamber 21.Specifically, the pressing means 25 includes a hydraulic cylinder 26that is supportively mounted on an unillustrated support frame providedat the upper side of the upper electrode 220 and a piston rod 27 eachprojecting downward from the hydraulic cylinder 26.

An insulator 28 is provided between the piston rod 27 and the upperelectrode 220 to connect the pressing means 25 and the upper electrode220 in a mutually and electrically insulated state. In this embodiment,the insulator 28 is, for instance, formed of a polyacetal resin or asilicon resin.

The heating medium supply means 470 includes a heated air supply unit470 a for supplying heated air into the food loading chamber 21, and acooling water supply unit 470 b for supplying cooling water into thefood loading chamber 21. The supply unit 470 a has an air compressor 472for raising the air pressure at a level of about 3 kg/cm², a first highpressure pipe 474 provided between the air compressor 472 and the lowerelectrode 210, a control valve 476 provided at the first high pressurepipe 474, and a boiler 478 provided between the control valve 476 andthe air compressor 472 for heating the air inside the food loadingchamber 21 up to a temperature in the range of 110 to 140° C.

The boiler 478 is so constructed as to heat the pressurized air of about3 kg/cm² supplied from the air compressor 472 up to a temperature in therange of 110 to 140° C. using electric power or heat of combustionobtained by burning a fuel such as gas or petroleum as a heat source.Feedback controlling the boiler 478 based on a detection value of anunillustrated temperature sensor and pressure sensor enables supplyingheated air of the above-mentioned pressure and temperature into the foodloading chamber 21 by opening the control valve 476.

The cooling water supply unit 470 b includes a second high pressure pipe482 connected to the first high pressure pipe 474 downstream of thecontrol valve 476, a pressurizing pump 484 for feeding high-pressurizedcooling water (of about 3 kg/cm²) into the second high pressure pipe482, and a control valve 48 provided at the second high pressure pipe482 downstream of the pressurizing pump 484.

A drainage pipe 480 with a base end thereof communicated inside the foodloading chamber 21 and a distal end thereof opened to the outside air isprovided on the lower electrode 210. A control valve 490 is provided onthe way of the drainage pipe 480. The food loading chamber 21 sealablyclosed by the upper electrode 220 communicates outside by opening thecontrol valve 490. Opening the control valve 490 releases the sealedstate of the food loading chamber 21 and ejects heated air or coolingwater staying inside the chamber 21 out of the food loading container 2.The cooling water may be water, such as tap water, of ambienttemperature or cool water with a temperature lower than the ambienttemperature.

When the control valve 486 is closed and the air compressor 472 isdriven in a state that the control valve 476 is opened, heated air issupplied into the food loading chamber 21 and drawn out of the foodloading container 2 via the control valve 490. In this way,high-pressurized heated air of 1 atm or higher communicates in and outof the food loading chamber 21. On the other hand, when the controlvalve 476 is closed and the pressurizing pump 484 is driven with anopened state of the control valve 490, and then, the control valve 486is opened, high-pressurized cooling water is supplied into the foodloading chamber 21. Thereby, the heated air inside the food loadingchamber 21 is replaced with the incoming cooling water while maintainingthe high-pressurized state.

The temperature adjusting means 400 includes a steam generator 410having a boiler and the like, a cooling water supply source 420 such aswaterworks, a lower electrode temperature adjusting pipe 430 embedded inthe lower electrode 210 in a winding manner, and an upper electrodetemperature adjusting pipe 440 embedded in the upper electrode 220 alsoin a winding manner.

The steam generator 410 has a steam supply main pipe 410 a for drawingout generated steam. The main pipe 410 a is branched into two sub pipes410 b at a downstream end thereof. The respective sub pipes 410 b areconnected to an upstream end of the pipes 430, 440. Further, an upstreamend of a cooling water supply source 420 a is connected to the supplysource 420, and the main pipe 420 a is branched into two sub pipes 420 bat a downstream end thereof. Downstream ends of the respective sub pipes420 b are connected to the pipes 430, 440. A flexible tube made of asynthetic resin (not shown) is provided at an appropriate position onthe way of the sub pipes 410 b, 420 b to insulate an upstream portionthereof from the opposing electrode pair 20.

A control valve 450 is provided at the main pipe 410 a, and a controlvalve 460 is provided at the supply source 420 a. Opening and closingthe control valves 450, 460 changeably supplies steam from the steamgenerator 410 and cooling water from the supply source 420 to the pipes430, 440 to adjust the temperature of the container 2 y and consequentlythe temperature of the prepackaged food Pa loaded in the chamber 21.

A downstream end of the pipes 430, 440 is formed into an open endopening outward. Steam and cooling water supplied through the pipes 430,440 are drawn out of the pipe system through the open end afteradjusting the temperature of the container 2 y.

An inner wall of the pipes 430, 440 is covered with an insulator toprevent the water and steam passing through the pipes 430, 440 frombeing adversely affected electrically.

The food sterilizing apparatus 106 of the sixth embodiment is operatedin the similar manner as the control sequence (FIG. 5) by the controlsystem 700 (see FIG. 4) similar to the first embodiment except for thetemperature raising step X21. Specfically, in the temperature raisingstep X21 of this embodiment, heated air is supplied to the chamber 21simultaneously with driving of the high frequency generating means 3.Thereby, a high frequency power from the high frequency generating means3 is supplied between the lower electrode 210 and the upper electrode220, and the temperature of the prepackaged food Pa is, as shown in FIG.4B, raised rapidly by dielectric heating, while a non-contact area ofthe prepackaged food Pa which is not rendered in contact with theopposing electrode pair 2 is heated with heated air. When thetemperature of the prepackaged food Pa reaches a predeterminedtemperature (e.g., in the range of 110 to 140° C.), the driving of thehigh frequency generating means 3 is suspended, and the sequenceproceeds to the heating step X22.

In the heating step X22, the temperature of the prepackaged food Pa iskept at a predetermined temperature (e.g., in the range of 110 to 140°C.) for a predetermined time period by steam supply from the steamgenerator 410 and heated air supply from the boiler 478 to substantiallyperform heat sterilization to the prepackaged food Pa by maintaining thetemperature for the predetermined time period. Upon completion of theheat sterilization in the heating step X22, the primary cooling step X23is executed.

In the primary cooling step X23, the control valve 450 is closed to stopsupply of steam from the steam generator 410 to the food loadingcontainer 2 y. Then, the control valve 460 is opened to supply coolingwater from the supply source 420 to the pipes 430, 440. Thereby, asshown in FIG. 5B, the temperature of the prepackaged food Pa in the foodloading chamber 21 is lowered down to the temperature at 100° C. orbelow. Then, the control valve 490 is opened to drain the water insidethe food loading chamber 21 out of the pipe system. This coolingoperation prevents long stay of the food at such a temperature that maycause growth of bacteria. This is effective in preventing re-growth ofbacteria in the prepackaged food Pa.

After the temperature of the prepackaged food Pa is lowered to 100° C.or below in the primary cooling step X23, then, in the take-out step X3,the upper electrode 220 is raised followed by lifting up of the pistonrod 27 by activation of the hydraulic cylinder 26 to open up the foodloading chamber 21. Then, the prepackaged food Pa is taken out from thefood loading chamber 21, put in the secondary cooling step X4 where theprepackaged food Pa is immersed in cooling water filled in theunillustrated water bath to lower the temperature thereof to an ambienttemperature. The above-mentioned each step in accordance with batchprocessing is cyclically repeated in the food sterilizing apparatus 1 tosequentially perform heat sterilization to the prepackaged foods Pa.

As mentioned above in detail, the food sterilizing apparatus 106 of thesixth embodiment is so designed as to supply high -pressurized heatedair, in the sterilizing step X2, from the heating medium supply means470 into the airtight food loading chamber 21 in which the prepackagedfood Pa is loaded. In this arrangement, the non-contact area on theouter surface of the prepackaged food Pa which is not rendered incontact with the opposing electrode pair 20 is heated by heated air,while a high frequency from the high frequency generating means 3 isapplied to the prepackaged food Pa loaded inside the food loadingchamber 21 in a held state by the opposing electrode pair 20 to heat theinside of the prepackaged food Pa by electromagnetic wave. Since theperipheral portion of the prepackaged food P which could not have beensufficiently heated by electromagnetic wave is heated with heated air inthis embodiment, heating by combination of heated air andelectromagnetic wave enables uniform heating of the inside theprepackaged food Pa. Consequently, avoided is an uneven state of heatedtemperature inside the prepackaged food Pa, which was unavoidable whenheating the prepackaged food solely depending on application ofelectromagnetic wave, as in the conventional method. Thereby,well-balanced sterilization is securely performed while performinguniform heat maturation of the prepackaged food Pa to eliminatevariation of flavors and tastes of the prepackaged food Pa

FIGS. 12A and 12B are cross sections showing a seventh embodiment of afood sterilizing apparatus 107, FIG. 12A showing a state that an upperelectrode 220 is raised, and FIG. 12B showing a state that the upperelectrode 220 is lowered. As shown in FIGS. 12A and 12B, in the seventhembodiment, the food sterilizing apparatus 107 has a metallic pressingplate 29 indirectly attached to a ceiling of the upper electrode 220which is operably pressed against the upper side of the prepackaged foodPa The configuration of the upper electrode 220 is the same as the sixthembodiment except that the pressing plate 29 is provided in the seventhembodiment. Specifically, the pressing plate 29 is attached to theceiling of the upper electrode 220 by way of a pair of spring members 29a each bent into a substantially V-shape in side view. The pressingplate 29 has a length slightly smaller than the transverse size of afood loading chamber 21. The pressing plate 29 is housed in the foodloading chamber 21 encased by a sealing member 23 x when the upperelectrode 220 is lowered. The other arrangement of the seventhembodiment is similar to the sixth embodiment.

A connecting piece 29 b which electrically connects the upper electrode220 and the pressing plate 29 is provided between the pair of springmembers 29 a. The connecting piece 29 b is provided by bending a thincopper plate into a U-shape in side view. The connecting piece 29 b isso designed as to set the distance between the pressing plate 29 and theupper electrode 220 variable in accordance with a deflected amount(elastic deformation) of the connecting piece 29 b, and apply a highfrequency from the upper electrode 220 onto the pressing plate 29uniformly.

According to the food sterilizing apparatus 107 of the seventhembodiment, the pressing plate 29 is located, as shown in FIG. 12A,projectingly below the upper electrode 220 due to the spring members 29a when the upper electrode 220 is raised upward. When the piston rod 27is lowered by driving a hydraulic cylinder 26 from this state, thepressing plate 29 is accommodated in the food loading chamber 21 abovethe lower electrode 210 and comes into pressing contact with the upperside of the prepackaged food Pa when the upper electrode 220 is renderedinto contact with the sealing member 23 x. At this time, a compressiveforce of the spring members 29 a against the spring force is increased,thus leading to a downwardly pressed state of the prepackaged food Pa.In this state, the pressing plate 29 functions as the upper electrode.

Providing the pressing plate 29 enables coping with a variation of thethickness of the prepackaged food Pa, even if such variation occurs, dueto elastic deformation of the spring members 29 a. This arrangementimproves usability of the food sterilizing apparatus 107.

FIG. 13 is a schematic cross section showing an eighth embodiment of thefood sterilizing apparatus according to the invention. Although thearrangement of a sealing member 23 x and an upper electrode 220 of anopposing electrode pair 20 b of the eighth embodiment is the same as thesixth embodiment, the eighth embodiment is different from the sixthembodiment in that a lower electrode 210 b of the opposing electrodepair 20 b is shaped into a container with a closed bottom by forming arecess 210 c at a center on an upper surface thereof to fittingly load acup-shape prepackaged food Pa therein.

According to the food sterilizing apparatus 108 of the eighthembodiment, forming the recess 210 c in the lower electrode 210 bincreases the height dimension of the food loading chamber 21. Thereby,this arrangement is applied to the prepackaged food Pa of a cup-shapevessel which has a certain height dimension, and improves usability ofthe food sterilizing apparatus 108.

In the eighth embodiment, the recess 210 c is formed in the lowerelectrode 210 b. Alternatively, the recess may be formed in a bottomside of the upper electrode, or may be formed both in the upper andlower electrodes.

FIG. 14 is a schematic cross section showing a ninth embodiment of thefood sterilizing apparatus according to this invention. This embodimentis an alteration of the seventh embodiment. A lower pressing plate 291is supported on the side of a lower electrode 210 by way of a certainnumber of bar-shape support members 293, and likewise, an upper pressingplate 292 is supported on the side of a ceiling of an upper electrode220 by way of a certain number of bar-shape support members 293 at aposition opposing to those on the lower pressing plate 291. In thisarrangement, a prepackaged food Pa is pressingly held between the lowerand upper pressing plates 291, 292 when the prepackaged food Pa isloaded in a food loading chamber 21. The lower and upper plates 291, 292are electrically connected to the lower and upper electrodes 210, 220,respectively. A high frequency voltage applied to the lower and upperelectrodes 210, 220 is applied to the prepackaged food Pa via the lowerand upper pressing plates 291, 292.

In this embodiment, each of the support members 293 is formed into ametallic bar-shape. As an alternative, the support member 293 may beformed of an elastic member such as a coil spring to cope with avariation of thickness of the prepackaged food Pa held by the pressingplates 291, 292 using elasticity of the elastic member. The otherarrangement of the ninth embodiment is the same as the food sterilizingapparatus 106 (see FIGS. 10, 11A, 11B) of the sixth embodiment.

According to the food sterilizing apparatus 109 of the ninth embodiment,when the prepackaged food Pa is pressingly held by the pressing plates291, 292 in the food loading chamber 21, and a heating medium or acooling medium is drawn into the food loading chamber 21 to attainuniform heating aided by auxiliary heating or cool the prepackaged foodPa, the prepackaged food Pa is supported spaced away from an inner wallof the food loading chamber 21. Accordingly, an efficient auxiliaryheating and efficient cooling is performed by transmission of theheating medium through the pressing plates 291, 292 and direct heatexchange of the heating medium.

Hereafter, basic two types of prepackaged food loading container appliedto a serially operated (including semi-serially operated) sterilizingapparatus according to this invention is described with reference toFIGS. 15 to 20B. Next, an alteration of container of the basic type isdescribed with reference to FIGS. 21 to 24, and a sterilizing apparatusfor sterilizing a prepackaged food loaded in the altered container isdescribed with reference to FIGS. 25 to 30. A power supply systemdifferent from the one shown in FIGS. 25 to 29 is described withreference to FIGS. 17A and 17B. A container of another type and asterilizing apparatus for sterilizing a prepackaged food loaded in theanother type of container is described with reference to FIGS. 18 to 22.

FIGS. 15 and 16 are perspective views showing a first modification ofthe container according to this invention, FIG. 15 showing a state thata cover is opened, and FIG. 16 showing a state that the cover is closed.FIGS. 17A and 17B are cross sections taken along the line A—A in FIG.16, FIG. 17A showing a state that the cover is opened, and FIG. 17Bshowing a state that the cover is closed. In FIGS. 15 and 16, X—Xdirection represents widthwise direction of the food loading container,and Y—Y direction represents depth direction thereof. Specifically, −Xdirection indicates leftward direction, +X direction indicates rightwarddirection, and −Y direction indicates forward direction, and +Ydirection indicates rearward direction.

As shown in FIGS. 15 and 16, the container 1 essentially includes anannular container main body (annular frame) 2 made of a non-conductivematerial, a bottom plate 3 made of a conductive material for closing anopening at a bottom side of the container main body 2, and a cover 4 foropenably closing an opening at a top side of the container main body 2.The container main body 2 corresponds to the annular insulator 23 or thesealing member 23 x shown in FIGS. 1 to 14.

The container main body 2 is made of a polytetrafluoroethylene excellentin heat resistance and durability. A food loading chamber 21 for loadinga prepackaged food P is defined in the container main body 2 by an innerwall of the container main body 2 and the bottom plate 3. The foodloading chamber 21 is brought to a sealed state by closing the cover 4.

An O-ring 22 made of a synthetic rubber is attached to an upper end ofthe container main body 2 to securely keep the sealed state of the foodloading chamber 21 when the food loading chamber 21 is closed by thecover 4. In this modification, the O-ring 22 is provided. However, asfar as the sealability of the food loading chamber 21 in the containermain body 2 is ensured, the O-ring 22 may be omitted.

In this modification, the prepackaged food P is such that a certain kindof food is packed in a food container body P1 of a rectangular-shapetray in plan view, as shown in FIG. 15. The food container body P1 isformed with an annular rim P2 projecting outward from an upper endthereof. After the food is loaded in the food container body P1, asynthetic resin sheet P3 is adhered to the annular rim P2 by, forinstance, thermal fusion to sealably pack the food in the food containerbody P1.

The inner dimension of the container main body 2 is set at such athree-dimensional configuration as to match the outer shape of the foodcontainer body P1. In this arrangement, when the prepackaged food P isloaded in the food loading chamber 21, the bottom side of theprepackaged food P comes into contact with the bottom plate 3, and theouter side surface of the prepackaged food P comes into contact with theinner side wall of the container main body 2. When the cover 4 is closedafter the prepackaged food P is loaded in the food loading chamber 21, aceiling of the cover 4 comes into contact with the synthetic resin sheetP3 of the prepackaged food P. In this way, the entire outer surface ofthe prepackaged food P comes into contact with the entire inner wall ofthe prepackaged food loading container 1.

As shown in FIGS. 17A and 17B, the bottom plate 3 has a pair of lowerhinges 31 each of an L-shape provided at the Y—Y directional oppositeends projecting outward from a left side thereof. The cover 4 has a pairof upper hinges 41 each of an L-shape corresponding to the pair of lowerhinges 31. A bolt B is inserted in a hole formed in a lead end of thelower hinge 31 and upper hinge 41 in a jointed state and tightened witha nut N to rotatably joint the cover 4 to the bottom plate 3 about anaxis of the bolt B. The hinge pairs 31, 41 are molded of an engineeringplastic having a certain rigidity, which is a non-conductive material,to insulate the space between the bottom plate 3 and the cover 4.

As shown in FIGS. 16, 17A and 17B, the bottom plate 3 is internallyformed with a winding-shaped lower fluid passage 32, and likewise, thecover 4 is internally formed with a winding-shaped upper fluid passage42. A fluid drawing connector 33 is mounted on a right side of thebottom plate 3 in FIGS. 17A, 17B (−Y direction in FIG. 15) tocommunicate with the lower fluid passage 32, and a fluid ejectingconnector 34 is mounted on the right side of the bottom plate 3 in FIGS.17A, 17B at a position corresponding to the fluid drawing connector 33(+Y direction in FIG. 15) to communicate with the lower fluid passage32. In this arrangement, a fluid drawn into the lower fluid passage 32through the connector 33 is ejected out of the connector 34 afterpassing through the winding-shaped passage 32. A valve is provided ateach of the connectors 33, 34, 43, 44. Controlling opening/closing ofthe valves enables switching between connection and disconnection of theconnectors 33, 34, 43, 44 to and from the food loading chamber 21.

Similarly, the cover 4 is mounted with the fluid drawing connector 43and the fluid ejecting connector 44 which communicate the upper fluidpassage 42. A fluid drawn into the upper fluid passage 42 through thefluid drawing connector 43 is ejected out of the fluid ejectingconnector 44 after passing along the upper fluid passage 42.

The fluid drawing connectors 33, 43 and the fluid ejecting connectors34, 44 are so connected to a hot water source and a cooling watersource, as is described in the following section describing asterilizing process of the prepackaged food P, to draw hot water intothe fluid passages 32, 42 before dielectric heating in order to promoteheating of the prepackaged food P loaded in the food loading chamber 21by heat transmission, and then to draw cooling water into the fluidpassages 32, 42 after the dielectric heating in order to lower thetemperature of the prepackaged food P once raised in the food loadingchamber 21.

A pair of connecting tabs 35 respectively projecting leftward andrightward are provided on widthwise opposite ends of the bottom plate 3.The connecting tab pair 35 each provided at a number of prepackaged foodloading containers 1 arrayed at the same interval is fixed on a conveyorbelt 13 by a bolt B. In this arrangement, the prepackaged food loadingcontainers 1 are serially moved forward by driving the conveyor belt 13.The conveyor belt 13 defines a transport path for the prepackaged foodloading containers 1 according to this invention.

An operable projecting tab 45 projecting leftward is provided on anupper left end of the cover 4. Pushing a lead end of the operableprojecting tab 45 downward opens up the cover 4, and releasing thepushing force allows the cover 4 to close the top opening of the foodloading chamber 21.

According to the prepackaged food loading container 1 of the firstmodification, when the cover 4 is closed after loading the prepackagedfood P in the chamber 21, the outer side surface of the food containerbody P1 comes into close contact with the inner side wall of the chamber21. Also, the bottom surface and the top surface of the food containerbody P1 are respectively rendered into close contact with the bottomplate 3 and the cover 4. In addition, the annular rim P2 is held betweenan upper peripheral end of the food loading chamber 21 and the cover 4.In this arrangement, the prepackaged food P is securely held by theopposing electrode pair applied with a high frequency at a certainpressing force without a possibility of pop-up of the cover 4.Accordingly, even if the prepackaged food P is heated at the temperatureof 100° C. or higher by application of a high frequency from theopposing electrode pair, avoided is a problem that the food containerbody P1 is burst out due to boiling and vaporizing of water contained inthe prepackaged food P.

FIGS. 18 and 19 are perspective views of the container as a secondmodification according to this invention, FIG. 18 showing a state that acover is opened, and FIG. 19 showing a state that the cover is closed.FIGS. 20A and 20B are cross sections taken along the line B—B in FIG.19, FIG. 20A showing a state that the cover is opened, and FIG. 20Bshowing a state that the cover is closed. The directionality of thecontainer in FIGS. 18 and 19 is the same as the description in FIGS. 15and 16.

The arrangement of the container 1 a in the second modification is thesame as the container 1 in the first modification except that: a foodloading chamber 21 a of a container main body 2 a in the secondmodification is not necessarily formed with such an inner shape as tomatch the three-dimensional configuration of the prepackaged food Pa; alocking means (open restricting means) 36 for holding a closed state bythe cover 4 is provided in the second modification; and the container 1a is so designed as to draw a fluid (heated air and cooling water) intothe food loading chamber 21.

The food loading chamber 21 a of the container main body 2 a is notspecifically designed to match the three-dimensional shape of a specificprepackaged food, but rather shaped into a rectangular parallelepiped toaccommodate a prepackaged food of versatile shape. As an example, abag-type prepackaged food Pa is shown in FIG. 18.

The locking means 36 is provided at a widthwise right end of a bottomplate 3. The locking means 36 includes a bracket 37 projecting outwardfrom a center on the right end of the bottom plate 3, a pivot tab 38that pivots about a first horizontal axis 37 a while holding the bracket37 at split two leg portions thereof, and a locking tab 39 that pivotsabout a second horizontal axis 38 a while holding a lead end of thepivot tab 38 at split two leg portions thereof.

An operable tab 38 b projecting outward from the pivot tab 38 through aspace between the leg portions of the locking tab 39 is provided at aright end of the pivot tab 38. Pressingly operating the operable tab 38b in such a manner as to rotate the pivot tab 38 in a specifieddirection about the first horizontal axis 37 a rotates the locking tab39 up and down.

An engaging portion 39 a curved in counterclockwise direction about thesecond horizontal axis 38 a is formed at a distal end of the locking tab39. A plate-shape insulator 47 is provided at an upper right end of thecover 4 at a position corresponding to the engaging portion 39 a. Anengaging projection 47 a for engaging with the engaging portion 39 a isformed at a lead end of the insulator 47. When the operable tab 38 b isrotated clockwise about the first horizontal axis 37 a in a state thatthe cover 4 is closed and the engaging portion 39 a is engaged with theengaging projection 47 a, a base end of the locking tab 39 is lowered,as shown in FIGS. 19 and 20B, while maintaining the insulated state ofthe bottom plate 3 and the cover 4 by the insulator 47. Thereby, theclosed state of the food loading chamber 21 a is locked in a state thatthe second horizontal axis 38 a is set slightly leftward of the firsthorizontal axis 37 a. In this arrangement, even if the inside of thefood loading chamber 21 is brought to a high-pressurized state of 1 atmor higher, the sealed state of the food loading chamber 21 ismaintained, thus eliminating leakage of a high-pressurized fluid.

On the other hand, when the operating tab 38 b is rotatedcounterclockwise about the first horizontal axis 37 a from the closinglocked state by the cover 4 shown in FIGS. 19 and 20B, the locking tab39 is lifted up while releasing the engagement of the engaging portion39 a with the engaging projection 47 a to unlock the closed state of thefood loading chamber 21 a by the cover 4.

When the food loading chamber 21 a is set in the lock released state, asshown in FIGS. 18 and 20A, the pivot tab 38 is set in a horizontalposture by a biasing force of an unillustrated bias means, whereas thelocking tab 39 is set in a substantially vertical posture by a biasingforce of an unillustrated bias means. In this arrangement, the lockingmeans 36 is securely set at a certain position when the food loadingchamber 21 a is set in a lock released state to facilitate lockingoperation by the locking means 36.

In this modification, the locking means 36 is so designed as towithstand a high-pressurized state of the food loading chamber 21 a evenif the inner pressure of the prepackaged food P loaded in the foodloading chamber 21 a is raised at a level of about 3 kg/cm². Thisarrangement makes it possible to suppress expansion of the prepackagedfood Pa even if the temperature of the prepackaged food Pa is raised ata temperature in the range of 110° C. to 140° C. by dielectric heating.

A fluid drawing connector 330 and a fluid ejecting connector 340 areprovided at a widthwise left end of the bottom plate 3. A fluid drawinghole 331 communicating with the fluid drawing connector 330 and a fluidejecting hole 341 communicating with the fluid ejecting connector 340are formed in an upper surface of the bottom plate 3 opposite the foodloading chamber 21 a. In this arrangement, a fluid is drawn in and outof the food loading chamber 21 a through the connectors 330, 340 and theholes 331, 341. A valve is provided at the connectors 330, 340.Controlling opening/closing of the valves switchingly connects anddisconnects the connectors 330, 340 to and from the food loading chamber21 a.

A pair of timing belts 130 each formed with meshable teeth on theunderside surface thereof and extending in the Y direction are providedas a conveyor belt for conveying the prepackaged food loading containers1 a. The timing belts 130 define a transport path for the containersaccording to this invention. A connecting terminal for application ofhigh frequency is rendered into contact with an exposed part on thebottom plate 3 of the container 1 a which is exposed between the belts130 while conveyed to a certain position over the timing belts 13 toallow the bottom plate 3 to function as one of opposing electrodes.

According to the prepackaged food loading container 1 a of the secondmodification, when the cover 4 is closed and locked by the locking means36 after the prepackaged food Pa is loaded in the food loading chamber21 a, and the valves of the connectors 330, 340 are closed after ahigh-pressurized fluid is drawn into the food loading chamber 21 a, theinside of the food loading chamber 21 a is brought to a sealed state. Inthis arrangement, even if the temperature of the prepackaged food Pa inthe food loading chamber 21 a is raised high by dielectric heating, andthe inside of the food loading chamber 21 a is set in a high-pressurizedstate, the cover 4 does not pop up. This arrangement eliminates anecessity of providing an electrode pair to pressingly hold the bottomplate 3 and the cover 4 during dielectric heating and simplifies theconstruction of the unit for dielectric heating.

Further, when a high-pressurized heated air is drawn into the foodloading chamber 21 a in the sealed state through the fluid drawingconnector 330, a peripheral end of the prepackaged food Pa which ishardly rendered into contact with the opposing electrode pair is heatedto perform auxiliary heating. Thereby, eliminated is a possibility ofuneven heat transmission over the prepackaged food Pa which may cause anincomplete sterilization of the prepackaged food Pa.

Also, after the dielectric heating, cooling water is drawn into the foodloading chamber 21 a through the fluid drawing connector 330 and drawnout of the food loading chamber 21 a through the fluid ejectingconnector 340. In this arrangement, cooling of the prepackaged food Pais quickly performed to lower the temperature thereof to 100° C. orlower in a short time. This arrangement enables to open the cover 4after the dielectric heating within a short time, which improves heatsterilization efficiency.

FIG. 21 is a cross section showing essential parts of the prepackagedfood loading container as a third modification according to thisinvention. The container 1 b of the third modification includes, asshown in FIG. 21, a bottom plate 3 a, a container main body 2 b, and acover 4 a each made of a synthetic resin, namely, a non-conductivematerial. A food loading chamber 21 b for loading a prepackaged food P(Pa) is defined by the bottom plate 3 a, the container main body 2 b,and the cover 4 a.

A lower electrode 30 for applying a high frequency is mounted on thebottom plate 3 a of the food loading chamber 21 b, and an upperelectrode 40 for applying a high frequency is mounted on the cover 4 aof the chamber 21 b. When the cover 4 a is closed after the prepackagedfood P (Pa) is loaded in the chamber 21 b, the prepackaged food P (Pa)is held between the electrodes 30, 40. The other arrangement of thecontainer 1 b in this modification is the same as the container 1 (1 a)of the first (second) modification.

According to the container 1 b of the third modification, since almostall parts constituting the container 1 b is made of a synthetic resin,the light weight container 1 b is obtained.

FIG. 22 is a cross section showing essential parts of the container as afourth modification according to this invention. The container 1 c ofthe fourth modification is, as shown in FIG. 22, made of a metallicmaterial and formed together with a bottom plate 3 b. According to thisarrangement, since an inner wall of a container main body 2 c itselffunctions as a lower electrode, a lower electrode 30 shown in the thirdmodification is omitted in this modification. A food loading chamber 21b for loading a prepackaged food P (Pa) is defined by the inner wall ofthe container main body 2 c and a bottom surface of a cover 4 a. Whenthe cover 4 a is closed after the prepackaged food P (Pa) is loaded inthe chamber 21 b, the prepackaged food P (Pa) is rendered into contactwith an upper electrode 40 and the inner wall of the container main body2 c functioning as the lower electrode. The other arrangement of thecontainer 1 c is the same as the container 1 (1 a) of the first (second)modification.

According to the container 1 c of the fourth modification, a side end ofthe prepackaged food P (Pa) is rendered into contact with the inner sidewall of the container main body 2 c functioning as an electrode to heatthe side end of the prepackaged food P (Pa) by dielectric heating, whichis generally difficult to be heated by dielectric heating. Thisarrangement is effective in uniformly heating the prepackaged food P(Pa). Also, since the container main body 2 c is made of a metallicmaterial, the resistance against high pressure is great, which enablesproducing a compact container main body 2 c, resulting in productioncost reduction for the container.

FIG. 23 is a cross section showing essential parts of the container as afifth modification according to this invention. The container 1 d of thefifth modification is, as shown in FIG. 23, provided with a cover 4 b ofa metallic material, and accordingly a bottom surface of the cover 4 bfunctions as an upper electrode. On the other hand, a container mainbody 2 d is made of a synthetic resin with a closed bottom and formedwith a top opening. A plurality of support members 203 with a verticallength identical to each other are provided on a bottom plate 3 c of thecontainer main body 2 d. Each support member 203 projects inward in afood loading chamber 21 c. A plate-shape lower electrode 201 issupported on top parts of the support members 203.

The support member 203 is, in this modification, made of an elasticmember such as a coil spring and a plate spring. Elastic deformation ofthe support members 203 absorbs a variation of the thickness of aprepackaged food P (Pa) loaded in the chamber 21 c, with an uppersurface of the prepackaged food P (Pa) coming into close contact withthe cover 4 b and a bottom surface thereof coming into close contactwith an upper surface of the lower electrode 201. The other arrangementof the container 1 d is substantially the same as the container 1 (1 a)of the first (second) modification.

According to the container 1 d of the fifth modification, when the cover4 b is closed after the prepackaged food P (Pa) is loaded in the chamber21 c of the container main body 2 d, the mounted state of theprepackaged food P (Pa) in the chamber 21 c is stabilized since avariation of the thickness of the prepackaged food P (Pa), even if suchvariation occurs, is absorbed by the support members 203 made of theelastic member. Further, since the prepackaged food P (Pa) is pressinglyheld between the cover 4 b and the lower electrode 201 c, dielectricheating of the prepackaged food P (Pa) is securely performed.

Similar to the prepackaged food loading container 1 b of the secondmodification, it may be preferable to provide a fluid drawing connector330 and a fluid ejecting connector 340 on an outer wall of the containermain body 2 d to draw heated air into the chamber 21 c through theconnector 330 before and during dielectric heating, and then eject theair drawn out of the chamber 21 through the connector 340. In this way,passing the heated air through the chamber 21 c promotes heating a sideend of the prepackaged food P (Pa), which is difficult to be heated bydielectric heating, to enable uniform heating of the prepackaged food P(Pa).

FIG. 24 is a cross section showing essential parts of the container as asixth modification according to this invention. The container 1 e in thesixth modification includes, as shown in FIG. 24, a cover 4 a made of asynthetic resin similar to the third modification (see FIG. 21), and acontainer main body 2 d similar to the fifth modification. Similar tothe fifth modification, a lower electrode 201 is provided on the side ofa bottom plate 3 c of the container main body 2 d by way of supportmembers 203, and an upper electrode 202 is provided on the side of abottom surface of the cover 4 a as opposed the lower electrode 201 byway of support members 203. The other arrangement of the sixthmodification is substantially the same as the fifth modification.

According to the container 1 e of the sixth modification, the container1 e is entirely made of a synthetic resin except the electrodes 201,202. Accordingly, the light weight container 1 e is produced in additionto the operation and effect obtained by the container 1 d of the fifthmodification. This enables saving power necessary for transporting thecontainers. Also, since the prepackaged food P (Pa) is held by theelectrodes 201, 202 applied with a vertical pressing force, thisarrangement can flexibly cope with a variation of the thickness of theprepackaged food P (Pa), which enables heat sterilization of differenttypes of prepackaged foods P (Pa).

According to this arrangement, when performing auxiliary heating orcooling the prepackaged food P (Pa) by introducing a heating medium or acooling medium into the food loading chamber 21 c, the prepackaged foodP (Pa) is supportively held by the electrodes 201, 202 away from aninner wall of the food loading chamber 21 c, which assures efficientauxiliary heating and cooling.

As stated above, drawing the heating medium and cooling medium into thechamber 21 c suffices auxiliary heating and cooling of the prepackagedfood P (Pa). This arrangement eliminates a necessity of providing apassage in the cover 4 a and the container main body 2 d for passing theheating medium or cooling medium, which contributes to cost reduction ofthe container 1 e.

In the sixth modification, the container main body 2 d may be made of ametallic material. This alteration improves resistance of the container1 e against high pressure and reduces the production cost of thecontainer, compared to the one made of a synthetic resin with greatresistance against high pressure.

FIG. 25 is a perspective view showing a food sterilizing apparatus 110(tenth embodiment) using the container 1 of the first modification. Itshould be noted that X—X direction in FIG. 25 is widthwise direction ofthe apparatus, and Y—Y direction is depthwise direction of theapparatus. Particularly, −X direction is leftward direction, and +Xdirection is rightward direction. −Y direction and +Y directionrespectively become forward (downstream) direction and rearward(upstream) direction when referring to a forward belt. On the otherhand, −Y direction and +Y direction respectively become upstreamdirection and downstream direction when referring to a backward belt.

As shown in FIG. 25, the food sterilizing apparatus 110 includes a beltconveyor 11 with a transport plane set horizontal. The belt conveyor 11is so designed as to transport a plurality of containers 1 in a certaindirection, a prepackaged food loading mechanism 5, a preheatingmechanism 6, a dielectric heating unit 7, a cooling mechanism 8, and aprepackaged food takeout mechanism 9 in this order along the beltconveyor 11 from upstream to downstream.

The belt conveyor 11 includes a pair of rotary drums 12 disposedopposing each other in the forward and rearward direction of the beltconveyor 11, a conveyor belt 13 mounted between the rotary drums 12, andan electric motor 14 for driving the rotary drum 12. A forward locatedrotary drum 12 a is a drive drum, and a rearward located rotary drum 12b is a driven drum. Rotating the drive drum 12 a clockwise about a driveshaft thereof by the electric motor 14 circulatively moves the conveyorbelt 13 between the drive drum 12 a and the driven drum 12 b inclockwise direction.

The belt conveyor 11 includes a belt member made of a synthetic resinwith an insignificantly small dielectric loss and high rigidity. In thisembodiment, the belt conveyor 11 is made of polytetrafluoroethylene. Aplurality of containers 1 are arrayed at the same interval on thetransport plane of the belt conveyor 11 with the projecting direction ofan operable projecting tab 45 thereof normal to the driving direction ofthe conveyor belt 13. In this arrangement, when the conveyor belt 13 isdriven by the electric motor 14, the containers 1 are moved along theconveyor belt 13 between the rotary drums 12 followed by the movement ofthe conveyor belt 13.

It should be noted that hereinafter an upper side of the conveyor belt13 that is moved forward is referred to as a “forward belt 13 a”, and alower side thereof that is moved backward is referred to as a “backwardbelt 13 b”.

The loading mechanism 5 is provided on the upstream side with respect totransport of the forward belt 13 a, and includes a loading device 51 forloading a prepackaged food P into a chamber 21 of the container 1, and acover drive means 52 for openably closing a cover 4 of the container 1.The loading device 51 includes an unillustrated storage unit for storinga certain number of prepackaged foods P, and a loading actuator fortaking out a certain number of prepackaged foods P stored in the storageunit as a group to load the group of prepackaged foods P into therespective chambers 21 of the containers 1. In this embodiment, threeprepackaged foods P are loaded in corresponding three containers 1 atone time.

The cover drive means 52 includes a cylinder device 53 each providedwith a piston rod projecting downward, and an operable rod 54 connectedto the piston rods. The operable rod 54 has such a length as to coverthe group of containers 1 arrayed in a row on the forward belt 13 a in astate that the operable projecting tabs 45 of the group of containers 1oppose against the operable rod 54 simultaneously. In this arrangement,when the piston rods are lowered, the operable rod 54 simultaneouslypresses the operable projecting tabs 45 of the group of containers 1downward to simultaneously open up the covers 4 thereof, as shown inFIG. 25. On the other hand, by releasing the pressing force against theoperable projecting tabs 45 followed by lifting up of the piston rods,the covers 4 are closed.

Driving/suspending drive of the electric motor 14, opening/closing ofthe covers 4 of the group of containers 1 by driving the cover drivemeans 52, and loading of the prepackaged foods P into the chambers 21 ofthe group of containers 1 are performed synchronously at a certaintiming. Thereby, when a group of prepackaged foods P reach a certainposition at a prepackaged food loading location R1, the group ofprepackaged foods P are automatically loaded in the correspondingchambers 21 of the containers 1 simultaneously.

The preheating mechanism 6 includes a hot water source 61 provided withan unillustrated boiler and a delivery pump, a hot water pipe 62disposed communicable between the hot water source 61 and the group ofcontainers 1 that are moved to a preheating location R2 downstream ofthe loading location R1, and a connector means 63 provided at a lead endof the hot water pipe 62.

The hot water pipe 62 is branched into six sub pipes 62 a at a distalend thereof. Each pair of sub pipes 62 a are disposed at such a positionas to oppose fluid drawing connectors 33, 43 (see FIG. 17) provided at abottom plate 3 and the cover 4 of the container 1 respectively when thegroup of containers 1 are moved to the preheating location R2.

The connector means 63 is for connecting the sub pipes 62 a to thecorresponding connectors 33, 43. Driving the connector means 63switchingly connects and disconnects the sub pipes 62 a to and from theconnectors 33, 43, and controllably opens and closes valves of theconnectors 33, 43, 34, 44. In this arrangement, hot water from the hotwater source 61 is drawn into a lower fluid passage 32 formed in each ofthe bottom plates 3 and an upper fluid passage 42 formed in each of thecovers 4 to preheat the group of prepackaged foods P loaded in thechambers 21 by way of the bottom plates 3 and the covers 4.

The dielectric heating unit 7 includes a high frequency generator 71, anopposing electrode pair 72 consisting of an upper electrode 72 a and alower electrode 72 b to which a high frequency generated from the highfrequency generator 71 is applied so as to heat the group of prepackagedfoods P loaded in the containers 1, and a cylinder device 73 for movingthe upper electrode 72 a up and down. The opposing electrode pair 72 isso arranged as to interpose the forward belt 13 a therebetween at aposition on a heating/cooling location R3 downstream of the preheatinglocation R2 when the group of containers 1 are moved to theheating/cooling location R3. The lower electrode 72 b is so arranged asto render an upper surface thereof in contact with the forward belt 13a. In this embodiment, the opposing electrode pair functions as an openrestricting means according to this invention.

A group of three prepackaged food loading containers 1 that have beenpreheated at the pre-heating location R2 are fed to the heating/coolinglocation R3 by intermittent driving of the electric motor 14. At thistime, the upper electrode 72 a is lifted up by driving of the cylinderdevice 73. The group of containers 1 are then pressingly held betweenthe opposing electrode pair 72 by lowering of the upper electrode 72 a.In this state, a high frequency from the high frequency generator 71 isapplied to the prepackaged foods P in the group of containers 1 by wayof the opposing electrode pair 72, the bottom plates 3 and the covers 4of the containers 1 to perform heat sterilization onto the prepackagedfoods P by dielectric heating.

In this embodiment, the pressing force by the upper electrode 72 a iscontrolled to withstand an inner pressure of the prepackaged food P atabout 3 kg/cm² when loaded in the chamber 21 of the container 1. In thisarrangement, expansion of the prepackaged food P is suppressed even ifthe temperature of the prepackaged food P is raised as high in the rangeof 110 to 140° C. due to dielectric heating.

The cooling mechanism 8 is for cooling the group of prepackaged foods P,after having been completed with heat sterilization by the dielectricheating unit 7 at the heating/cooling location R3, while pressinglyholding the group of prepackaged foods P by the upper electrode 72 a atthe same location. The cooling mechanism 8 includes a cooling watersource 81, a cooling water pipe 82 disposed communicable between thecooling water source 81 and the group of containers 1, and a connectormeans 83 arranged at a distal end of the cooling water pipe 82. Thereason for cooling the group of prepackaged foods P at the same locationas the dielectric heating was conducted while pressingly holding theprepackaged foods P by the upper electrode 72 a is to prevent a problemthat the prepackaged food P may be expanded by releasing the pressingforce by the upper electrode 72 a against the prepackaged food loadingcontainer 1 which may result in burst out of a container main body P1 ofthe prepackaged food P.

The cooling water pipe 82 is branched into six sub pipes 82 a at adistal end thereof. Each pair of sub pipes 82 a are disposed at such aposition as to oppose the fluid drawing connectors 33, 43 (see FIG. 17)provided at the bottom plate 3 and the cover 4 of the container 1respectively when the group of containers 1 are moved to theheating/cooling location R3.

The connector means 83 is for connecting the sub pipes 82 a to thecorresponding connectors 33, 43. Driving the connector means 83switchingly connects and disconnects the sub pipes 82 a to and from theconnectors 33, 43, and controllably opens and closes the valves of theconnectors 33, 43, 34, 44. In this arrangement, cooling water from thecooling water source 81 is drawn into the lower fluid passage 32 formedin each of the bottom plates 3 and the upper fluid passage 42 formed ineach of the covers 4 to be replaced with the water staying in thepassages 32, 42 to cool the prepackaged foods P in the chambers 21 byway of the bottom plates 3 and the covers 4.

The above cooling operation is continued until the temperature of theprepackaged foods P is lowered from about 130° C. to 100° C. or below.When the temperature of the prepackaged foods P is lowered to 100° C. orbelow, holding of the prepackaged food P by the upper electrode 72 a isreleased, and the group of containers 1 are fed to the take-outmechanism 9 by driving of the electric motor 14. A guide cover 15 with acertain portion in parallel with the transport plane of the conveyorbelt 13 is disposed above the conveyor belt 13 with a certain distance.The guide cover 15 has a certain length covering an outer circumferencearea of the drive drum 12 a up to the take-out mechanism 9 forpreventing the cover 4 from opening up even when the prepackaged foodloading container 1 is being fed upside down from the forward belt 13 ato the backward belt 13 b.

The prepackage d food take-out mechanism 9 is for taking out theprepackaged food P that has been cooled by the cooling mechanism 8 fromthe container 1 and immersing the prepackaged food P in water forcooling. The take-out mechanism 9 includes a cooling bath 91 disposed ata certain position at a take-out location R4 below the backward belt 13b, and a discharge belt 92 with a certain portion thereof immersed inthe cooling water filled in the cooling bath 91. The discharge belt 92circulates in and out of the cooling water in the cooling bath 91 bydving of an unillustrated drive means. In this arrangement, theprepackaged food P that has been immersed in the cooling water in thecooling bath 91 is emerged out of the cooling bath 91 and dischargedoutside.

A heating medium shown by the solid black arrow in FIG. 25 may bepreferably drawn into t he upper electrode 72 a and the lower electrode72 b, and discharged out therefrom as shown by the blank arrow. In thisarrangement, the upper electrode 72 a and the lower electrode 72 b areheated to promote heating of the group of prepackaged foods P in thecontainers 1 in addition to dielectric heating in order to improve thesterilizing efficiency. Also, a heating medium may be introduced intothe upper electrode 72 a and the lower electrode 72 b during dielectricheating, and then a cooling medium may be introduced into the upperelectrode 72 a and the lower electrode 72 b upon completion of thedielectric heating. Thereby, the group of prepackaged foods P aftersterlization are rapidly cooled to prevent a problem that theprepackaged food P is exposed to a temperature state that may inducegrowth of bacteria for a long time.

The upper electrode 72 a may be divided into three sections toindividually supply a high frequency power to the group of threeprepackaged foods P from compact high frequency generating devices. Inthis arrangement, the group of prepackaged foods P disposed between theopposing electrode pair 20 a may be uniformly applied with a highfrequency power.

FIG. 26 is a block diagram showing an example of a control system of thefood sterilizing apparatus 110. As shown in this drawing, the controlsystem 700 includes a control means 710 for centrally controlling anoperation of the apparatus 110, and an operating unit 120 for operatingthe dielectric heating unit 7 and the apparatus 110.

The control means 710 controls power supply to a high frequencygenerator 71 of the dielectric heating unit 7 based on operation datainputted by way of the operating unit 120, and is designed to output acertain control signal to the loading mechanism 5, the preheatingmechanism 6, and the cooling mechanism 8 to control driving thereof.

The operating unit 120 has an operation button section 123 provided witha start-up button 121, a stop button 122, etc., as well as a data enterkey 124 for inputting various data such as the kind and volume of theprepackaged food P, the cycle for intermittently driving the electricmotor 14, and the cycle for operating the loading mechanism 5 and thepreheating mechanism 6.

An operation signal from the start-up button 121 and the stop button 122is outputted to the control means 710 as a control signal via thecontrol means 710. When the start-up button 121 is operated, driving ofthe high frequency generator 71 starts, as well as initiatingdriving/operation of the electric motor 14, the loading mechanism 5, thepreheating mechanism 6, the cooling mechanism 8, and the prepackagedfood take-out mechanism 9. On the other hand, when the stop button 122is operated, the driving of the high frequency generator 71 issuspended, and the driving of the various parts including the electricmotor 14 is suspended.

The high frequency generator 71 includes a power circuit 71 a, a highfrequency generating circuit 71 b for generating a high frequency uponpower supply from the power circuit 71 a, and a rectifying circuit 71 cprovided downstream of the circuit 71 b. The power circuit 71 a is fortransforming a power of e.g., 220V for commercial use to a directcurrent power of a predetermined level. The circuit 71 b is of aself-oscillating type which generates a high frequency energy of adesired level upon supply of a DC voltage of the predetermined levelfrom the power circuit 71 a. The high frequency generating circuit 71 bmay be of an enforced oscillating type. The rectifying circuit 71 c is acircuit for rectifying a current balance between the circuit 71 b and acurrent passing through a load (prepackaged food P) disposed between theopposing electrode pair 20, and includes a transformer 71 d and anunillustrated capacitor for rectification. A coil, or a capacitor and acoil may be used for rectification, in place of the capacitor.

The control means 710 is programmed to compute a desired power supplylevel that is obtained in advance based on experiments conducted undervarious conditions of differentiated kind, volume and thickness of theprepackaged food P. The computation is executed based on data inputtedthrough the data enter key 124. An output power from the power circuit71 a is set based on a computation result of the inputted data

The electric motor 14 is driven at a certain time interval based on acontrol signal from the control means 710. Thereby, the conveyor belt 13circulates intermittently in such a manner that the conveyor belt 13moves by a distance corresponding to a group of three prepackaged foodsloading containers 1 by one feeding operation. In this arrangement, eachtime when the conveyor belt 13 moves, the group of containers 1 thathave been set at the loading location R1 are fed to the preheatinglocation R2, the preceding group of containers 1 that have been locatedat the preheating location R2 are fed to the heating/cooling locationR3. In this way, each group of containers 1 are moved to the nextdownstream operating location R2 (R3).

During the movement of the conveyor belt 13, the loading mechanism 5,the preheating mechanism 6, and the cooling mechanism 8 are set in astand-by mode. Namely, these mechanism 5, 6, 8 stay still relative tothe group of containers 1, and the upper electrode 72 a of thedielectric heating unit 7 is raised to allow the containers 1 to passbetween the opposing electrode pair 72. On the other hand, when themovement of the conveyor belt 13 is suspended, the loading mechanism 5,the preheating mechanism 6, and the cooling mechanism 8 are driven toperform a certain operation to the group of containers 1, and thedielectric heating unit 7 performs heating operation to the prepackagedfoods P in the group of loading containers 1 by driving the highfrequency generator 71 while the group of containers 1 are pressinglyheld between the opposing electrode pair 72 by lowering of the upperelectrode 72 a. The discharge belt 92 of the take-out mechanism 9 iscontrolled to constantly drive during an ON-state of the start-up button121.

FIGS. 27A and 27B are diagrams showing a sequence of heat sterilizationperformed by the tenth food sterilizing apparatus 110 using the firstmodified prepackaged food P, FIG. 27A showing the sequence of steps, andFIG. 27B being a graph showing a relation between the temperature of theprepackaged food P in each step from a preheating step Q2 to a coolingstep Q5 and time. As shown in FIG. 27A, the food sterilizing apparatus110 is operated to sequentially perform a loading step Q1 of loading theprepackaged food P in the chamber 21 of the container 1, the preheatingstep Q2 of preheating (auxiliary heating) the container 1 in which theprepackaged food P is loaded, a temperature raising step Q3 of raisingthe temperature of the preheated prepackaged food P, a sterilizing stepQ4 of sterilizing the prepackaged food P by maintaining the temperatureof the prepackaged food P that has been raised at a certain point in thetemperature raising step Q3, the cooling step Q5 of cooling thesterilized prepackaged food P, and a take-out process Q6 of taking outthe cooled prepackaged food P from the food loading chamber 21.

The loading step Q1 is performed when the prepackaged food P is moved atthe loading location R1 of the apparatus 110, the preheating step Q2 isperformed when the prepackaged food P is moved to the preheatinglocation R2, the temperature raising step Q3, the sterilizing step Q4and the cooling step Q5 are performed when the prepackaged food P ismoved to the heating/cooling location R3, and the take-out step Q6 isperformed when the prepackaged food P is moved to the takeout locationR4.

Hereafter, each step is described with reference to an arbitrary one ofthe containers 1 that are intermittently moved over the conveyor belt13. When the container 1 reaches the loading location R1, the loadingstep Q1 is executed. Specfically, the operable rod 54 is lowered bydriving of the cylinder devices 53. Then, the operable projecting tab 45of the container 1 that stays still at the loading location R1 ispressed downward to open up the cover 4 thereof. Next, driving theloading device 51 enables the prepackaged food P to be loaded into thechamber 21. After the loading, the operable rod 54 is raised by drivingthe cylinder devices 53. Then, the cover 4 is closed to set the foodloading chamber 21 in a closed state.

Next, driving of the conveyor belt 13 moves the container 1 to thepreheating location R2 downstream of the loading location R1. Thereupon,driving of the conveyor belt 13 is suspended, and the connector means 63is operated to communicate the hot water sub pipes 62 a with the fluiddrawing connectors 33, 43 (see FIG. 17) of the bottom plate 3 and thecover 4 of the container 1 that stays still at the preheating locationR2.

In this state, hot water from the hot water source 61 is supplied to thefluid passages 32, 42 of the bottom plate 3 and the cover 4 anddischarged out of the pipe system through the opened fluid ejectingconnectors 34, 44. Passing of the hot water preheats the prepackagedfood P in the chamber 21 by way of the bottom plate 3 and the cover 4.The preheating step Q2, as shown in FIG. 27B, raises the temperature ofthe prepackaged food P from an ambient temperature up to about 40° C.The preheating time in the preheating step Q2 lasts for about 240 to 360seconds.

Next, upon completion of the preheating by the preheating step Q2, thecontainer 1 is moved to the heating/cooling location R3 by driving theconveyor belt 13. Then, suspending drive of the conveyor belt 13 andlowering the upper electrode 72 a by driving the cylinder devices 73that are executed simultaneously pressingly holds the container 1between the opposing electrode pair 72. In this state, performed is thetemperature raising step Q3 where the temperature of the prepackagedfood P is raised up to about 130° C. by driving the high frequencygenerator 71, and then, the sterilizing step Q4 for maintaining thetemperature at about 130° C. is performed. The process time in thetemperature raising step Q3 lasts for about 90 seconds, and the processtime in the sterilizing step Q4 lasts for about 30 seconds.

Since the process time required for sterilization varies depending onthe output of the high frequency generator 71, the weight of theprepackaged food, and the sterilizing temperature, it is required to setthe sterilizing process time in advance considering these parameters.For instance, in the case where a normal prepackaged food is to besterilized, an experiment proved that a complete sterilization isenabled within several seconds, which is remarkably shorter comparedwith the above sterilizing process time (30 seconds) if the sterilizingtemperature is set as high as about 140° C., 10° C. higher than 130° C.

In the latter half of the temperature raising step Q3 and in thesterilizing step Q4, the prepackaged food P in the chamber 21 is heatedas high as 100° C. or higher. At this time, however, the prepackagedfood P is pressingly held by the opposing electrode pair 72, and theinner wall of the chamber 21 is kept in close contact state with theouter surface of the prepackaged food P. Accordingly, the boiling pointof water inside the prepackaged food P is raised, and prevented is waterboiling and burst-out of the prepackaged food P.

Next, upon completion of the sterilization at the temperature raisingstep Q3, the cooling step Q5 is performed onto the prepackaged food Pthat is still pressingly held by the opposing electrode pair 72. In thisstep, first, driving the connector means 83 connects the cooling watersub pipes 82 a to the fluid drawing connectors 33, 43. Then, the coolingwater from the cooling water source 81 is drawn into the fluid passages32, 42. Thereby, the temperature of the prepackaged food P in thechamber 21 is lowered to a point slightly lower than 100° C. due tosupply of the cooling water by way of the bottom plate 3 and the cover4. The process time in the cooling step Q5 lasts for about 120 to 180seconds.

Next, upon completion of the cooling in the cooling step Q5,simultaneous driving of the cylinder devices 53 to lift up the upperelectrode 72 a and driving of the conveyor belt 13 allows the container1 to move onto the back side of the conveyor belt 13, namely, from theforward belt 13 a to the backward belt 13 b. Then, intermittent drivingof the conveyor belt 13 eventually releases the container 1 from theholding control by the guide cover 15 (see FIG. 25) when the container 1is moved to the takeout location R4. Then, the cover 4 of the container1 is opened up by the weight thereof to release the prepackaged food Ploaded in the chamber 21 into the water filled in the cooling bath 91.Then, the discharged prepackaged food P is immersed in the water in thecooling bath 91 to lower the temperature thereof to a substantiallyambient temperature, and carried out of the discharge belt 92. The emptycontainer 1 is then returned to the loading location R1 by circulationof the conveyor belt 13.

In this way, according to the first modification of the food sterilizingapparatus 110, intermittent transport of the container 1 by intermittentdriving of the conveyor belt 13 enables to automatically andsequentially execute the followings in the order named: loading theprepackaged food P into the container 1 in the loading step Q1; raisingthe temperature thereof up to a preheat temperature in the preheatingstep Q2; raising the temperature thereof up to a sterilizing temperaturein the temperature raising step Q3; sterilizing the prepackaged food Pin the sterilizing step Q4; lowering the temperature thereof to 100° C.or lower in the cooling step Q5; and taking out the prepackaged food Pthat has been cooled down to the substantially ambient temperature inthe take-out step Q6. This is effective in improving sterilizingefficiency of the prepackaged food P.

FIG. 28 is a perspective view showing a food sterilizing apparatus 111(eleventh embodiment) using the container 1 a of the secondmodification. It should be noted that X—X direction in FIG. 28 iswidthwise direction of the apparatus, and Y—Y direction is depthwisedirection of the apparatus. Particularly, −X direction is leftwarddirection, and +X direction is rightward direction. −Y direction and +Ydirection respectively become forward (downstream) direction andrearward (upstream) direction when referring to a forward belt. On theother hand, −Y direction and +Y direction respectively become upstreamdirection and downstream direction when referring to a backward belt.

In the eleventh embodiment, the container 1 a provided with a cover lockmechanism of locking the closed state by the cover 4 is adopted. In thisconstruction, since the closed state by the cover 4 is secured in astate that the prepackaged food Pa is loaded in the container 1 a, thereis no need of providing an arrangement of pressingly holding the cover 4in order to prevent open-up of the cover 4 during dielectric heating.Accordingly, simplified is the construction of applying a high frequencyto the prepackaged food Pa by a dielectric heating unit 7 a, althoughthe cover locking/unlocking mechanism for the container 1 a is provided.Further, since the inside of the chamber 21 of the container 1 isbrought to a sealably closed state by the cover locking mechanism,high-pressure heated air for preheating can be introduced into thechamber 21.

In this embodiment, a belt conveyor (container moving means) 11 a forcirculating the containers 1 a includes, as shown in FIG. 28, a pair oftiming belts 130 each mounted between the drive drum 12 a and the drivendrum 12 b provided side by side in the widthwise direction of the drum.Providing the pair of timing belts 13 in the widthwise direction of thedrum allows a certain bottom portion of the bottom plate 3 of thecontainer 1 a to be exposed outward between the timing belts 130 torender the exposed portion in contact with a lower terminal for highfrequency application which is described below.

A loading/locking location R11, a pressurizing/preheating location R12,and a dielectric heating location R13 are provided at a certain positionon a forward belt 130 a of the timing belt pair 130, each with a certainlength corresponding to a group of three containers 1 a in this orderfrom upstream side. A first cooling location R14, a second coolinglocation R15, and a take-out location R16 are provided at a certainposition on a backward belt 130 b of the timing belt pair 130, each witha certain length corresponding to the group of containers 1 a in thisorder from upstream side.

A prepackaged food loading mechanism 5 similar to the tenth embodimentis provided at the loading/locking location R11, and in addition, alocking mechanism 50 for locking a closed state by the cover 4 isprovided at the loading/locking location R11. After the prepackaged foodPa is loaded in the chamber 21 of the container 1 a by the loadingmechanism 5 and the cover 4 is closed, the locking mechanism 50 performsa predetermined operation to lock the closed state of the container 1 aby the cover 4. Specifically, the operable tab 38 b (see FIG. 20A) ofthe locking means 36 set in a horizontal posture is first rotatedcounterclockwise about the first horizontal axis 37 a to temporarilyallow the engaging portion 39 a of the locking tab 39 to cross over theengaging projection 47 a of the cover 4, and then rotating the operabletab 38 b clockwise engages the engaging portion 39 a with the engagingprojection 47 a.

A pressurizing/preheating mechanism 60 is provided at thepressurizing/preheating location R12 for supplying heated air into thechamber 21 where the prepackaged food Pa is sealably loaded. Thepressurizing/preheating mechanism 60 includes a heater 601 for heatingthe atmospheric air to hot air, a compressor 602 for pressurizing theheated air at about 3 atm to blow the pressurized heated air, a heatedair pipe 603 branched into three sub pipes 603 a at a downstream endthereof corresponding to three containers 1 a, and a connector means 604provided near the sub pipes 603 a.

The connector means 604 is operated to connect the sub pipes 603 a withthe respective fluid drawing connectors 330 of the group of containers 1a in such a way as to open and close the communication by way of thevalves, and connect the sub pipes 603 a with the respective fluidejecting connectors 340 of the group of containers 1 a in such a way asto open and close the communication by way of the valves. In thisarrangement, the pressurized heated air from the compressor 602 is drawninto the chambers 21 of the group of containers 1 a to directly preheatthe prepackaged foods Pa through communication of the pressurized heatedair.

Upon completion of the preheating, the connector means 604 is operatedto close the fluid drawing connectors 330 and the fluid ejectingconnectors 340. Thereby, the pressurized heated air sealably stays inthe chambers 21.

A dielectric heating unit 7 a and an external heating mechanism 80 areprovided at the dielectric heating location R13. The dielectric heatingunit 7 a includes a high frequency generator 71, an upper terminal 720 a(functioning as an upper electrode) for transmitting the high frequencygenerated from the high frequency generator 71 to the covers 4 of thegroup of containers 1 a, and a lower terminal 720 b (functioning as alower electrode) for transmitting the high frequency to the bottomplates 3 of the group of containers 1 a. The upper terminal 720 a has anelongated shape with a certain length extending in the circulatingdirection of the timing belts 130 and is rendered into contact with thecovers 3 of the group of containers 1 a that have been moved to thedielectric heating location R13. Likewise, the lower terminal 720 b isprovided between the timing belts 130 at a position vertically opposingthe upper terminal 720 a and rendered into contact with the bottomplates 3 of the group of containers 1 a that have been moved to thedielectric heating location R13.

In this arrangement, when the group of containers 1 that have reachedthe dielectric heating location R13 by circulation of the timing belts130, they are held by the upper terminal 720 a and the lower terminal720 b. Thereby, the prepackaged foods Pa in the respective containers 1a are subject to dielectric heating by way of the bottom plates 3 andthe covers 4.

The external heating mechanism 80 includes a boiler 801 for generatingsteam by heating water, a pump 802 for ejecting steam from the boiler801, a steam pipe 803 for drawing the steam from the pump 801 into thebottom plates 3 and the covers 4 of the group of containers 1 atransported at the dielectric heating location R13 by way of six subpipes 803 a branched at a downstream end thereof, and a connector means804 provided at a downstream end of the sub pipes 803 a.

The connector means 804 is operated to connect each pair of sub pipes803 a to the corresponding fluid drawing connector 330 and the fluidejecting connector 340 to open the valve thereof. Thereby, heated steamfrom the steam pipe 803 is drawn into the chambers 21 of the group ofcontainers 1 a. Upon completion of heat sterilization at the dielectricheating location R13, the connector means 804 is operated to close thevalve thereof to disconnect the steam pipe 803 with the fluid drawingconnectors 330 and the fluid ejecting connectors 340.

An upstream cooling mechanism 8 a similar to the cooling mechanism 8 ofthe tenth embodiment including a cooling water source 81, a coolingwater pipe 82, cooling water sub pipes 82 a, and a connector means 83 isprovided at the first cooling location R14. A downstream coolingmechanism 8 b similar to the upstream cooling mechanism 8 a is providedat the second cooling location R15. These cooling mechanisms 8 a, 8 bare for supplying cooling water from the cooling water source 81 intothe chambers 21 of the group of containers 1 a to directly cool theprepackaged foods Pa therein. Arranging the cooling mechanisms 8 a, 8 bin series manner enables obtaining a desired cooling effect even if theinterval of intermittent transport of the group of containers 1 isshortened. The cooling water source 81 is commonly used for the upstreamcooling mechanism 8 a and the downstream cooling mechanism 8 b in thisembodiment.

In this arrangement, when the group of containers 1 a are transported atthe dielectric heating location R13, heat sterilization is performed bythe dielectric heating unit 7 a. Next, when the group of containers 1 areach the first cooling location R14 by intermittent driving of thetiming belts 130, they are subjected to a first stage of cooling wherethe temperature thereof is lowered to an intermediate coolingtemperature (temperature slightly higher than 100° C.) by supply ofcooling water into the chambers 21 a by the upstream cooling mechanism 8a. Then, when the group of containers 1 a reach the second coolinglocation R15 by circulation of the timing belts 130, they are subjectedto a second stage of cooling where the temperature thereof is lowered to100° C. or below.

A lock release mechanism 90 and a prepackaged food take-out mechanism 9including a cooling bath 91 and a discharge belt 92 similar to theeleventh embodiment are provided at the take-out location R16. The lockrelease mechanism 90 is for releasing a locked state of the cover 4, andperforms a predetermined operation to the covers 4 of the group ofcontainers 1 a that have moved to the second cooling location R15.Specifically, the operable tab 38 b of the locking means 36 that is setin a horizontal posture (see FIG. 20B) is rotated counterclockwise tounlock the engagement of the engaging portion 39 a of the locking tab 39with the engaging projection 47 a of the cover 4. Thereby, the cover 4of the container 1 a loaded with the prepackaged food Pa is opened up bythe weight thereof to let the loaded prepackaged food Pa fall down.

Then, the discharged prepackaged food Pa is immersed into cooling waterfilled in the cooling bath 91 one after another to perform a final stageof cooling where the temperature thereof is lowered down to asubstantially ambient temperature, and discharged out of the apparatusby driving of the discharge belt 92. The empty container 1 a is returnedto the loading/locking location R11 by a circulative movement of thetiming belts 130.

FIG. 29 is a perspective view showing an alteration of the eleventh foodsterilizing apparatus 111 (food sterilizing apparatus 111 a). Thealtered food sterilizing apparatus 111 a is for sterilizing thetray-type prepackaged food P instead of the bag-type prepackaged foodPa. In this modification, adopted is a heating medium generatingmechanism 60 a having a steam boiler 601 a in place of thepressurizing/preheating mechanism 60. A heat exchange plate 991 isprovided at such a position as to come into contact with the covers 4 ofa group of three containers 1 a that have moved to a preheating locationR12′. Steam from the steam boiler 601 a is designed to draw into theheat exchanger plate 991 by way of a steam pipe 602 a. Thereby, prior todielectric heating at a dielectric heating location R13, the prepackagedfoods P in the group of containers 1 a are preheated.

A prepackaged food take-out mechanism 9 a includes a cooling pool 91 ahaving such a size as to immerse a lower half part of timing belt pair130 in water filled therein. The container 1 a is, after dielectricheating at the dielectric heating location R13, is immersed in coolingwater filled in the cooling pool 91 a by a circulative movement of thetiming belt pair 130. After the cooling, the container la has the cover4 opened up by a lock releasing mechanism 90 when moved to a take-outposition R15′ and is discharged out of the apparatus by driving of adischarge belt 92. The other arrangement is the same as the apparatus111 of the eleventh embodiment.

According to the altered apparatus 111 a, it is possible to preheat theprepackaged foods P in the containers 1 a by the heat exchange plate 991prior to dielectric heating. Thereby, sterilizing efficiency isimproved. In addition, the container 1 a after the dielectric heating isimmersed in water for cooling, which improves cooling efficiency.Consequently, sterilizing efficiency as a whole is improved.

FIG. 30 is a block diagram showing an example of a control system of theapparatus 111 as the eleventh embodiment. As shown in this drawing, thecontrol system of the apparatus 111 is similar to that of the apparatus110 of the tenth embodiment shown in FIG. 26 except that the container 1in the tenth embodiment is not provided with a locking means 36.Accordingly, a control operation concerning to the locking means 36 isnot provided in the tenth embodiment. On other hand, in the latterembodiment (eleventh embodiment), the locking means 36 is provided forthe container 1 a. Accordingly, the latter embodiment is different fromthe former embodiment (tenth embodiment) in that control relating to alocking/unlocking operation of the locking means 36 is effected.

In the eleventh embodiment, a high frequency is applied to the container1 a by way of the upper terminal 720 a that is not moved up and down andthe lower terminal 720 b. Accordingly, control concerning to up/downmovement of the upper electrode 72 a, as performed in the tenthembodiment, is not implemented.

A control signal for intermittently driving the electric motor 14 at acertain interval is outputted from a control means 710. Intermittentdriving of the timing belt pair 130 based on the control signalintermittently transports a group of containers 11. Respectivepredetermined control signals are outputted from the control means 710to the loading mechanism 5, the locking mechanism 50, thepressurizing/preheating mechanism 60, the dielectric heating unit 7 a,the upstream cooling mechanism 8 a, the downstream cooling mechanism 8b, and the lock releasing mechanism 90 in synchronism with drive suspendtiming of the group of containers 1 a, thereby allowing these mechanism5 to 90 to perform a predetermined operation. In this way, sterilizationdue to dielectric heating is automatically and sequentially effected tothe prepackaged foods Pa loaded in respective groups of containers 1 a.

The takeout mechanism 9 starts when the start-up button 121 is turned onand keeps on driving irrespective of drive/drive suspend state of thetiming belt pair 130, and suspends its driving when the stop button 122is operated.

FIGS. 31A and 31B are diagrams showing a heat sterilization performed bythe eleventh food sterilizing apparatus using the second modifiedprepackaged food. FIG. 31A is a diagram showing a sequence of steps, andFIG. 31B is a graph showing a relation between the temperature of theprepackaged food in each step from a preheating step to a cooling stepand time. As shown in FIG. 31A, the heat sterilization by the apparatus10 a includes, similar to the tenth embodiment, a loading step Q1′ ofloading the prepackaged food Pa in the chamber 21 a of the container 1,a preheating step Q2′ of preheating the container 1 a in which theprepackaged food Pa is loaded, a temperature raising step Q3′ of raisingthe temperature of the preheated prepackaged food Pa, a sterilizing stepQ4′ of sterilizing the prepackaged food Pa by maintaining thetemperature of the prepackaged food Pa that has been raised at a certainpoint in the temperature raising step Q3′, a cooling step Q5′ of coolingthe sterilized prepackaged food Pa, and a take-out step Q6′ of takingout the cooled prepackaged food Pa from the food loading chamber 21 a.

The loading step Q1′ is performed when the prepackaged food Pa is movedto the loading/locking location R11 of the food sterilizing apparatus 10a, the preheating step Q2′ is performed when the prepackaged food Pa ismoved to the pressurizing/preheating location R12, the temperatureraising step Q3′ and the sterilizing step Q4′ are performed when theprepackaged food Pa is moved to the dielectric heating location R13, thecooling step Q5′ is performed when the prepackaged food Pa is moved tothe first cooling location R14 and the second cooling location R15, andthe take-out step Q6′ is performed when the prepackaged food Pa is movedto the take-out location R16.

Hereafter, each step is described with reference to an arbitrary one ofthe containers 1 a that are intermittently moved to the respectivelocations by intermittent driving of the timing belts 130. When thecontainer 1 a reaches the loading/locking location R11, the loading stepQ1′ is executed. Specifically, the operable rod 54 is lowered by drivingthe cylinder devices 53. Then, the operable projecting tab 45 of thecontainer 1 a that stays still at the loading/locking location R11 ispressed downward to open up the cover 4 thereof. Next, driving theloading device 51 enables the prepackaged food Pa to be loaded into thechamber 21 a. After the loading, the operable rod 54 is raised bydriving the cylinder device 53. Then, the cover 4 is closed to set thechamber 21 a loaded with the prepackaged food Pa in a closed state.

Next, driving of the locking mechanism 50 locks the closed state of thecover 4 by a certain operation of the locking mechanism 50. Locking ofthe closed state is performed by moving the operable tab 38 b set in ahorizontal posture as follows. Specifically, the operable tab 38 b (seeFIG. 6A) of the locking means 36 set in a horizontal posture is firstrotated counterclockwise about the first horizontal axis 37 a totemporarily allow the engaging portion 39 a of the locking tab 39 tocross over the engaging projection 47 a of the cover 4, and thenrotating the operable tab 38 b clockwise engages the engaging portion 39a with the engaging projection 47 a. Thereby, the locking means 36 setsthe cover 4 in a locked state where the engaging portion 39 a engageswith the engaging projection 47 a as shown in FIG. 5, thereby settingthe inside of the food loading chamber 21 loaded with the prepackagedfood Pa in a sealably closed state.

Subsequently, driving of the timing belt pair 130 moves the container 1a to the pressurizing/preheating location R12 downstream of theloading/locking location R11. Thereupon, the driving of the timing beltpair 130 is suspended. At the pressuring/preheating location R12, thepreheating step Q2′ is performed. Specifically, the connector means 604is operated to communicate the steam sub pipes 603 a with the fluiddrawing connectors 33, 43 (see FIG. 6) of the bottom plate 3 and thecover 4 of the container 1 a that stays still at thepressurizing/preheating location R12.

In this state, heated air from the compressor 602 is supplied to thefluid passages 32, 42 of the bottom plate 3 and the cover 4 anddischarged out of the pipe system through the opened fluid ejectingconnectors 34, 44. Passing of the heated air preheats the prepackagedfood Pa in the chamber 21 a by way of the bottom plate 3 and the cover4. By the preheating step, as shown in FIG. 31B, the temperature of theprepackaged food Pa is raised from the ambient temperature to about 40°C. The preheating time in the preheating step Q2′ lasts for about 80 to120 seconds. The reason for setting the shorter preheating time in theeleventh embodiment, compared with the tenth embodiment, is because thehigh pressurized heated air is drawn into the chamber 21 a to directlypreheat the prepackaged food Pa. Immediately before completion of thepreheating step Q2′, the second fluid drawing connector 330 and thesecond fluid ejecting connector 340 are closed to set the inside of thechamber 21 in a sealably closed state filled with high pressurizedheated air.

Next, upon completion of the preheating by the preheating step Q2′, thecontainer 1 a is moved to the heating/cooling location R3 by driving ofthe timing belt pair 130. Upon drive suspend of the timing belt pair 130there at, the cover 4 is connected to the upper terminal 720 a, and thebottom plate 3 is connected to the lower terminal 720 b, therebyfunctioning the cover 4 and the bottom plate 3 substantially as anopposing electrode pair. In this state, driving the high frequencygenerator 71 enables effecting the temperature raising step Q3′ wherethe temperature of the prepackaged food Pa is raised to about 130° C.,and then, the sterilizing step Q4′ for maintaining the temperature atabout 130° C. is performed. In this embodiment, dielectric heating issuspended during the sterilizing step Q4′, accordingly, the sterilizingtemperature is maintained only by heat supply from an external heatingmechanism 80, which is described below. The process time in thetemperature raising step Q3′ lasts for about 60 to 90 seconds, and theprocess time in the sterilizing step Q4′ lasts for about 20 to 30seconds. To sum up, the total process time at the dielectric heatinglocation R13 is about 80 to 120 seconds by summation of the process timein the temperature raising step Q3′ and the sterilizing step Q4′ (seeFIG. 31B).

In the temperature raising step Q3′, auxiliary heating by the externalheating mechanism 80, in addition to dielectric heating by thedielectric heating unit 7 a, is performed onto the prepackaged food Pa.Specifically, when the container 1 a reaches the dielectric heatinglocation R13, the connector means 804 is operated such that the steamsub pipes 803 a are communicated with the fluid drawing connectors 33,43 of the bottom plate 3 and the cover 4, respectively to supply heatedair from the boiler 801 to the fluid passages 32, 42 (see FIG. 6).Thereby, the container 1 a is promoted with heating via the bottom plate3 and the cover 4. The auxiliary heating is continued until terminationof the sterilizing step Q4′.

In the latter half of the temperature raising step Q3′ and in thesterilizing step Q4′, the prepackaged food Pa in the chamber 21 a isheated as high as 100° C. or higher. At this time, however, the chamber21 a loaded with the prepackaged food Pa is set in a sealably closedstate with a locked state of the cover 4 by the locking means 36 towithstand a high pressurized state therein. Further, since thehigh-pressurized air at a high temperature prepared in the preheatingstep Q2′ is filled in the chamber 21 a. Accordingly, the boiling pointof water inside the prepackaged food Pa is raised, and thereby,prevented is water boiling and burst-out of the prepackaged food Pa.

Next, upon completion of the sterilization at the temperature raisingstep Q3′, the container 1 a reaches the first cooling location R14 by acirculative movement of the timing belt pair 130 to execute a firststage of cooling step Q5′ by the upstream cooling mechanism 8 a.Specifically, the upstream cooling mechanism 8 a is operated such thatdriving of the connector means 83 connects the cooling water sub pipes82 a to the second fluid drawing connectors 330 to draw the coolingwater from the water source 81 into the chamber 21 a via the secondfluid drawing connector 330. In this arrangement, the prepackaged foodPa in the chamber 21 a is subjected to the first stage of cooling wherethe temperature thereof is lowered to a temperature slightly lower than100° C. by supply of the cooling water. The process time by the upstreamcooling mechanism 8 a lasts for about 80 to 120 seconds (see FIG. 31B).

Next, the container 1 a is carried to the second cooling location R15 bydriving of the timing belt pair 130. Thereupon, the downstream coolingmechanism 8 b is operated, similar to the upstream cooling mechanism 8a, to perform a second stage of cooling step Q5′ to lower thetemperature of the prepackaged food Pa at about 90° C. The process timeby the downstream cooling mechanism 8 b lasts for about 120 to 180seconds (see FIG. 31B).

Next, upon completion of the cooling step Q5′, the timing belt pair 130is driven to move the container 1 a to the take-out location R16, wherethe lock releasing mechanism 90 drives the locking means 36 to set thecover 4 in a lock released state, as shown in FIG. 6A. Specfically, inthe lock released state, the cover 4 that has been set in the closedstate is opened up by the weight thereof to discharge the prepackagedfood Pa in the chamber 21 a into the water filled in the cooling bath91. The discharged prepackaged food Pa is immersed in the water to lowerthe temperature thereof to substantially the ambient temperature, andcarried out of the apparatus by the discharge belt 92. The emptycontainer 1 a is then returned to the loading/locking location R11 by acirculative movement of the timing belt pair 130.

In this way, according to the eleventh food sterilizing apparatus 10 a,intermittent transport of the timing belt pair 130 to intermittentlymove the container 1 a enables to automatically and sequentially executethe followings in the order named: loading the prepackaged food Pa intothe container 1 a in the loading step Q1′; raising the temperaturethereof up to a preheat temperature in the preheating step Q2′; raisingthe temperature thereof up to a sterilizing temperature in thetemperature raising step Q3′; sterilizing the prepackaged food Pa in thesterilizing step Q4′; lowering the temperature thereof to 100° C. orlower in the cooling step Q5′; and taking out the prepackaged food Pathat has been cooled down to the substantially ambient temperature inthe take-out step Q6′.

In the eleventh embodiment, the container 1 a provided with the lockingmeans 36 is used to let the locking means 36 lock the closed state ofthe cover 4 so as to set the inside of the food loading chamber 21 a ina sealably closed state. In this arrangement, the prepackaged food Pa isdirectly heated or cooled by introducing a heating medium into thechamber 21 a in the preheating step Q2′. Further, in the temperatureraising step Q3′ and the sterilizing step Q4′, even if the temperatureof the prepackaged food Pa is raised to 100° C. or higher, there can besecurely prevented a phenomenon that water inside the prepackaged foodPa is boiled, which may result in burst-out of the prepackaged food Padue to expansion of the prepackaged food Pa owning to boiling water.

Further, the cooling step Q5′ which rather takes a long time is dividedinto two stages: the first stage of cooling by the upstream coolingmechanism 8 a; and the second stage of cooling by the downstream coolingmechanism 8 b. In this arrangement, the time interval of intermittentdriving of the container 1 a combined with open-up operation of thecover 4 can be shortened, which is advantageous in improving the heatsterilization efficiency.

FIG. 32 is a diagram showing an alteration of the power supply system ofsupplying a high frequency power in the eleventh embodiment. In thispower supply system, the cover 4 of the container 1 a is provided with aplanar shape movable electrode 48 extending in a direction normal to themoving direction of the container 1 a and projecting horizontally. Atwo-legged fixing electrode 74 that enables the movable electrode 48 topass a space between the leg portions in non-contact state is provided.A high frequency power from the high frequency generator 71 is suppliedto the fixing electrode 74. The bottom plate 3 is grounded via a partconstituting the apparatus 10 a suitable for grounding.

According to the power supply system, the fixing electrode 74 and themovable electrode 48 are rendered into capacity coupling state at theirrespective opposing planes via a layer of air existing in the space.Therefore, a high frequency power from the high frequency generator 71is supplied to the prepackaged food P (Pa) without causing the electrodeunder high frequency application in contact with the container 1 a.Thereby, the power supply system is simplified, and omitted is acumbersome maintenance operation such as inspection as to whether theelectrode is reliably enabled in contact state with the container 1 a,and adjustment if a poor contact state is found.

FIGS. 33 and 34 are perspective views showing a twelfth embodiment ofthe food sterilizing apparatus according to this invention. FIG. 33shows a state that a cover is opened, and FIG. 34 shows a state that thecover is closed. FIG. 35 is a cross section taken along the line C—C inFIG. 34. Hereafter, X—X direction in FIGS. 33 and 34 is widthwisedirection of the apparatus, and Y—Y direction is depthwise direction ofthe apparatus. Particulaly, −X direction is “leftward direction”, +Xdirection is “rightward direction”, and −Y direction is “forwarddirection”, and +Y direction is “rearward direction”.

As shown in these drawings, a container 1 f includes a container manbody 2 e composed of a rigid insulating material similar to thecontainer main bodies 2, 2 a, 2 b, 2 c, 2 d of the modifications, abottom plate 3 d provided in a bottom portion of a food loading chamber21 d of the container main body 2 e, a metallic casing 209 covering anouter side surface and a bottom portion of the container main body 2 e,a cover 4 c for openably closing the chamber 21 d of the container mainbody 2 e, and a locking mechanism 500 for locking a closed state of thecover 4 c.

The container main body 2 e has, as shown in FIG. 33, a substantiallysquare shape in plan view, and is formed with the rectangularparallelepiped food loading chamber 21 d in the center thereof with asquare shape in plan view. An annular groove is formed in an upper endof the container main body 2 e to confine an O-ring 24 with an upperhalf part thereof exposed. A through-hole 250 (see FIG. 35) is formed ina center at the bottom portion of the chamber 21 d.

The bottom plate 3 d is made of a metallic flat plate, and is shapedinto a square so as to fit an outer peripheral end thereof in slidingcontact with an inner wall of the chamber 21 d. A downwardly projectingterminal rod 31 d is provided at a center on a bottom surface of thebottom plate 3 d, as shown in FIG. 35, corresponding to the through-hole250 with an outer diameter thereof smaller than an inner diameter of thethrough-hole 250.

The casing 209 includes a box shape main body 211 opened upward with asquare shape in plan view, and a pair of wings 212 projecting outward inwidthwise direction from an upper end of the widthwise lateral oppositeends of the casing main body 211. Each of the wings 212 is soconstructed as to set an upper surface thereof horizontal with athickness gradually decreased as approaching toward a lead end thereof.

A through-hole 213 with the same diametrical size as the through-hole250 is formed in a bottom portion of the casing main body 211corresponding to the through-hole 250 of the container main body 2 e.With the bottom plate 3 d mounted at the bottom portion in the chamber21 d of the container main body 2 e, the terminal rod 31 d is fittedinto the through-hole 250. Thereby, a distal end of the terminal rod 31d projects from the bottom portion of the container 1 f in an insulatedstate from the casing 209. A projected portion of the terminal rod 31 dis utilized as a connecting terminal 32 d for receiving a high frequencyfrom a high frequency generator 71.

An annular groove is also formed in an upper end of the casing 209, andan O-ring 24 is confined in the annular groove. When the cover 4 c isclosed, a bottom surface thereof comes into contact with two O-rings 24provided at the container main body 2 e and the casing 209. The doublecontact state with the O-rings 24 secures a sealably closed state of thechamber 21 d.

A fluid drawing connector 330 for drawing a heating medium into thechamber 21 d and a fluid ejecting connector 340 for ejecting the heatingmedium after passing through the chamber 21 d outward are provided at afront end of the casing main body 211. The connectors 330, 340 areprovided with control valves respectively to switchingly connect anddisconnect the inside of the food loading chamber 21 d to and from theoutside.

The cover 4 c has, as shown in FIG. 34, a square shape in plan view,similar to the casing 209, and is attached to the casing 209 by way of apair of hinges 41 c provided at the front end of the casing 209. In thisarrangement, the cover 4 c pivots about respective horizontal axes ofthe hinges 41 c to open and close the chamber 21 d. The cover 4 c isclosed by a biasing force of a bias means (not shown) in a normal state,and is opened only when releasably loading the prepackaged food Pa inthe chamber 21 d. It should be noted that the prepackaged food Pa innon-contact state with the inner wall of the chamber 21 d is illustratedin this modification. However, a prepackaged food P in close contactstate with the inner wall may be used.

To open up the cover 4 c, an operable projecting tab 45 is formed at afront end of the cover 4 c, and an operable rod 54 a which is projectedin and out by driving a drive means (not shown) is provided at anappropriate position on the transport path for the container 1 f. Whenthe operable projecting tab 45 of the container 1 f is pressed againstthe operable rod 54 a when the operable rod 54 a is set in a projectedstate, as shown in FIG. 33, the cover 4 c is opened up.

The cover 4 c has a flat bottom surface and a top surface formed with aslope 42 c at widthwise opposite ends thereof. The thickness of theslope 42 c (42 c) is gradually tapered as approaching a lead endthereof. A locked part 214 engageable with the locking mechanism 500,when the cover 4 c is closed, is formed by the tapered slope 42 c (42c).

The locking mechanism 500 includes a pair of hinges 510 provided at apart closer to a front part of the widthwise opposite ends of the casingmain body 211 projecting outward, and a pair of locking arms 550provided at widthwise ends each pivotally supported about a verticalaxis of the corresponding hinge 510. Each of the locking arms 550includes a rectangular parallelepiped main body 551, a projecting rod552 projecting in longitudinal direction of the arm main body 551 from alower end of the arm main body 551, and a pair of upper and lowerprojections 553 formed at a side surface of the arm main body 551extending in the longitudinal direction of the arm main body 551 toslidably receive the corresponding locked part 214. The locking arm 550is normally set in a lock released posture projecting widthwise from thecasing 209, as shown in FIG. 33, by a bias force of a bias means (notshown). On the other hand, when a dielectric heating is applied, thelocking arm 550 is retracted in a lockable state, as shown in FIG. 34,for locking a closed state of the cover 4 c.

The projecting rod 552 is so operated as to pivot the locking arm 550about the vertical axis 511 with a lead end thereof pivotally supportedby the vertical axis 511. The upper and lower projections 553 areoperated such that, in the case of operating the right (left) arm 550,the arm main body 551 is rotated counterclockwise (clockwise) about thevertical axis 511, as shown in FIG. 34, to hold the right (left) lockedpart 214 between the upper and lower locking projections 553. Thereby,the closed state of the cover 4 c is locked.

The projecting rod 552 is formed such that opposing planes thereof arerendered into sliding contact with the respective upper and lower slopesof the locked part 214. In this arrangement, when the locked part 214engages with the locking arm 550, the closed state of the chamber 21 cby the cover 4 c is secured.

The container 1 f is, as shown in FIGS. 33 to 35, constructed such thatthe bottom portion of the casing 209 is fixed to a pair of widthwiseprovided conveyor belts 131 of a food sterilizing apparatus 112 (alteredapparatus of the twelfth embodiment) to sterilize the prepackaged foodPa loaded in the chamber 21 d due to dielectric heating while moving thecontainer 1 f along a predetermined transport path defined by acirculative movement of the conveyor belt pair 131.

In this embodiment, the food sterilizing apparatus 112 is provided witha plurality of pressing roller pairs 16 arrayed in parallel with themoving direction of the conveyor belt pair 131 at a dielectric heatingregion R30. Each roller pair 16 is provided in widthwise direction ofthe apparatus. Each of the right-handed (left-handed) pressing rollers16 has its vertical axis 1 a supported on a common support member 17extending in forward/rearward direction, thereby allowing the pressingrollers 16 to freely rotate about the respective vertical axes 16 a. Thedistance between the pair of pressing rollers 16 opposing in widthwisedirection is set substantially the same as the distance between leadends of a pair of hinges 510 provided at the casing main body 211, andthe interval between the adjacent pressing rollers 16 arrayed inforward/rearward direction is set shorter than the length of the armmain body 551 in forward/rearward direction.

The food sterilizing apparatus 112 includes a terminal wire 18 providedbeneath the conveyor belt 131 in the lengthwise direction thereof at thedielectric heating region R30. A plus voltage of high frequency isapplied from the high frequency generator 71 to the terminal wire 18,whereas a minus voltage of high frequency is applied therefrom to thesupport members 17. In this arrangement, when the prepackaged food Pa isloaded in the chamber 21 d, and the container if set in a closed stateby the cover 4 c reaches the dielectric heating region R30 by driving ofthe conveyor belt pair 131, the pair of locking arms 550 which have beenset in the lock released posture, namely, in a projecting state from thecasing main body 211 first come into contact with the most upstream pairof pressing rollers 16. Accompanied by the forward movement of thecontainer 1 f, each of the locking arm pair 550 rotates rearward aboutthe vertical axis 511.

When the container 1 f is moved to the dielectric heating region R30, asshown in FIG. 34, the locked part 214 (see FIG. 35) of the container 1 fset in the closed state by the cover 4 c is pressingly held by the upperand lower projections 553 of the locking arm 550, with a connectingterminal 32 d of the terminal rod 31 d coming into contact with theterminal wire 18 (see FIG. 35). Thereby, a high frequency voltage fromthe high frequency generator 71 is applied to the prepackaged food Paloaded in the chamber 21 d via the bottom plate 3 d to performdielectric heating onto the prepackaged food Pa.

When the container 1 f is moved to the dielectric heating region R30,high pressurized heated air is supplied into the chamber 21 d via thefluid drawing connector 330 to raise the pressure inside the chamber 21d to 3 atm or higher. Thereby, prevented is burst-out of the prepackagedfood Pa, while propagating uniform heated state throughout theprepackaged food Pa aided by auxiliary heating onto the prepackaged foodPa.

According to the container 1 f as a seventh modification, the lockingarm 550 comes into sliding contact with the corresponding support member17 as the container 1 f is carried into the dielectric heating regionR30, thereby locking the closed state of the cover 4 c. Further, whilethe container 1 f moves out of the dielectric heating region R30, thelocked state is eventually released. In this arrangement, the lockingmechanism 500 for locking and unlocking is simplified, which contributesto installation cost reduction.

FIGS. 36 and 37 are diagrams illustrating a thirteenth embodiment of thefood sterilizing apparatus according to this invention. FIG. 36 is across-sectional side view, and FIG. 37 is a cross section taken alongthe line D—D in FIG. 36. In this modification, a prepackaged foodloading container 1 g (eighth modification) includes a container mainbody 2 (2 a) similar to the first (second) modification, a metallicbottom plate 3 e placed over a lower part of the container main body 2(2 a), a metallic intermediate plate 219 placed over a top part of thecontainer main body 2 (2 a), an insulating plate 230 placed over a toppart of the intermediate plate 219 and composed of the same material asthe container main body 2 (2 a), and a metallic cover 4 d placed over atop part of the insulating plate 230.

A food loading chamber 21 (21 a) for loading a prepackaged food P (Pa)is defined in the container main body 2 (2 a). When the intermediateplate 219, the insulating plate 230, and the cover 4 d are placed oneover the other in the predetermined order on the container main body 2(2 a) in a state that the prepackaged food P (Pa) is loaded in thechamber 21 (21 a), a sealably closed space is defined in the chamber 21(21 a). A pair of lower guide grooves 301 provided at widthwise ends(left-hand and right-hand direction on the plane of FIG. 37) eachextending in forward/rearward direction (leftward/rightward direction onthe plane of FIG. 36) are formed in a bottom portion of the bottom plate3 e of the container 1 g. A pair of upper guide grooves 401 are formedin a top surface of the cover 4 d in the similar manner as the lowerguide grooves 301.

A food sterilizing apparatus 113 (thirteenth embodiment) incorporatedwith the container 1 g includes plural pairs of lower rollers 191 witheach pair opposing in widthwise direction, plural pairs of upper rollers192 provided above the lower roller pairs 191 corresponding thereto, anda pushing member 193 for pushing the container 1 g to a dielectricheating region R31. The pushing member 193 is so constructed as toreciprocate in fore and aft direction by driving of a drive mechanism(not shown). When moved forward, the pushing member 193 pushes thecontainer 1 g toward the dielectric heating region R31 and passes itover the region R31.

The distance between widthwise centers of the lower roller pair 191 isset equal to the distance between widthwise centers of the opposinglower guide grooves 301. Thereby, as shown in FIG. 37, left and rightlower rollers 191 support the container 1 g in a fitted state in theleft and right lower guide grooves 301 to make the container 1 g movablein fore and aft direction.

At the dielectric heating region R31, the distance between widthwisecenters of the upper roller pair 192 is set equal to the distancebetween widthwise centers of the opposing upper guide grooves 401.Thereby, when the container 1 g is moved to the dielectric heatingregion R31 supported by the lower rollers 191, the inside of the chamber21 (21 a) is kept in a pressurized state while being pressed against theupper rollers 192 fitted in the upper guide grooves 401.

The upper roller 192 is constructed such that the height level thereofincreases as going upstream (right side in FIG. 36) of the dielectricheating region R31. In this arrangement, the container 1 g moved up tothe upstream side of the dielectric heating region R31 is readily pushedforward by the pushing member 193, thereby facilitating transport of thecontainer 1 g into the dielectric heating region R31.

When the container 1 g is pushed to the dielectric heating region R31, ahigh frequency voltage from a high frequency generator is applied to theprepackaged food P (Pa) in the chamber 21 (21 a) by way of theintermediate plate 219 and the bottom plate 3 e. Thereby, theprepackaged food P (Pa) is subjected to dielectric heating. In the caseof the prepackaged food Pa of a non-contact type that is not renderedinto contact with the inner wall of the container, pressurized heatedair is supplied into the chamber 21 a to promote heating, whilepreventing burst-out of the prepackaged food Pa

According to the container 1 g of the eighth modification, the inside ofthe chamber 21 (21 a) at the dielectric heating region R31 is renderedinto a sealably closed space without providing a complicated lockingmechanism for the container 1 g, which simplifies the construction ofthe container 1 g and reduces production cost for the container 1 g.

FIGS. 38A and 38B are diagrams showing a ninth modification of the foodloading container according to this invention. FIG. 38A is a plan view,and FIG. 38B is a cross sectional side view. In this modification, thefood loading container 1 h includes an upper-and lower-part-dividablecontainer main body 2 f composed of a synthetic resin such as epoxyresin, a metallic bottom plate 3 e constituting a bottom portion of thecontainer man body 2 f, and a top plate 4 e constituting a ceilingthereof.

The container main body 2 f includes a lower container main part(annular frame segment) 20 f and an upper container main part (anotherannular frame segment) 21 f. A through-hole for verticaly loading atray-type prepackaged food P is formed in the lower container main part20 f. When a lower part of the through-hole is closed by the bottomplate 3 e, a lower food loading chamber 21 x opened upward is defined ina center of the lower main part 20 f.

The lower food loading chamber 21 x has such an inner shape ofthree-dimensional size as to match the three-dimensional size of anouter shape of the prepackaged food P. An annular step portion 261 forfittingly receiving the annular end P2 is formed in an upper end of thelower chamber 21 x. When the tray-type prepackaged food Pa is loaded inthe lower chamber 21 x, an outer peripheral surface of the containermain body P1 comes into fitting contact with an inner wall of the lowerchamber 21 x with the annular end P2 fitted in the annular step portion261. Thereby, a top surface of the tray-type prepackaged food containerPa composed of a synthetic resin sheet P3 is set flush with a topsurface of the lower container main part 20 f.

The upper container main part 21 f is so constructed as to make thethickness (depth) thereof greater than the lower chamber 21 x and isformed with a recess at a lower part thereof so as to make the depth ofa three-dimensional configuration of the lower chamber 21 x set inupside-down state (corresponding to upper food loading chamber) slightlygreater than the lower chamber 21 x. Thereby, a ceiling 263 is formed onthe upper container main part 21 f. Mounting an upper electrode 40 of aflat plate shape in the recess (on the ceiling) and fixes the samedefines the upper food loading chamber 21 y for loading the tray-typeprepackaged food container Pa. A lower peripheral end of the upperchamber 21 y is formed with an annular step portion 262 corresponding tothe annular step portion 261 of the lower container main part 20 f. Inthis arrangement, loading the tray type prepackaged food container Paset in upside-down state in the upper chamber 21 y makes a bottomsurface of the synthetic resin sheet P3 of the prepackaged food P flushwith a bottom surface of the upper container main part 21 f.

Loading the tray type prepackaged food containers Pa in their respectivefood loading chambers 21 x, 21 y of the lower and upper chambers 21 x,21 y and jointly and pressingly holding the upper and lower containermain parts 21 f, 20 f with the chambers 21 x, 21 y opposing each otherenables sealably accommodating the two prepackaged foods Pa verticallyone over another in the container main body 2 f.

A through-hole 264 is formed in a center of the ceiling 263 of the uppercontainer main part 21 f and the top plate 4 e to expose a part of theupper electrode 40. A terminal for high frequency power application isconnected to the upper electrode 40 through the through-hole 264 tosupply a high frequency power to the upper electrode 40.

The bottom plate 3 e has a lower hinge 31 at one end thereof projectingoutward, and the top plate 4 e has an upper hinge 41 corresponding tothe lower hinge 31. When the upper and lower hinges 31, 41 are rotatablyjointed about their respective horizontal axes, the upper container mainpart 21 f is openably and closably jointed to the lower container mainpart 20 f.

The container main body 2 f has a locking means 380 on a side oppositethe side where the hinges 31, 41 are provided. The locking means 380includes a pair of brackets 381 each provided at an end of the bottomplate 3 e projecting outward, a locking rod 383 pivotally supportedabout a horizontal axis 382 interposed between the brackets 381, and arod operable tab 384 extending from a lower end of the locking rod 383branched into two-leg portions.

The locking rod 383 is formed with an engaging groove 383 a in a planeopposing the upper container main part 21 f. The engaging groove 383 ais formed in such a position as to confine a peripheral end of the topplate 4 e when the upper container main part 21 f is placed over thelower container main part 20 f.

In this arrangement, operating the rod operable tab 384 so as to rotatethe locking rod 383 clockwise about the horizontal axis 382 when theupper container main part 21 f is placed over the lower container mainpart 20 f fittingly receives the peripheral end of the top plate 4 e inthe engaging groove 383 a. Thereby, the closed state of the containermain body 2 f is locked. On the other hand, operating the rod operabletab 384 so as to rotate the locking rod 383 counterclockwise about thehorizontal axis 382 releases the locked state. The pivotal rotation ofthe locking rod 383 is executed by moving a piston rod up and down bydriving one of a pair of cylinder devices each provided at anappropriate position on a lower or upper side of a transport path forthe container main body 2 f.

According to the food loading container 1 f of the ninth modification,the upper electrode 40 is set in the upper chamber 21 y of the uppercontainer main part 21 f made of a synthetic resin, and a high frequencypower is supplied to the upper electrode 40 through the through-hole 264having a relatively large inner diameter. In this arrangement, thebottom plate 3 e, the lower hinge 31, the upper hinge 41, and thelocking means 380 are insulated from the upper electrode 40 with thecontainer main body 2 f of a synthetic resin interposed therebetween.Therefore, a problem can be avoided that a high frequency power isshort-circuited even if the upper and lower hinges 31, 41 and thelocking means 380 are made of a metallic material, thus making theconstruction of the food loading container 1 f durable.

Further, two prepackaged foods P can be loaded without heat variation inthe container main body 2 f. This improves sterilizing efficiency of theprepackaged food P.

In the food loading container 1 h of the ninth modification, it may bepossible to omit the locking means 380 and instead, a press machine maybe provided to pressingly hold the upper container main part 21 fagainst the lower container main part 20 f while a high frequency poweris supplied to the prepackaged food P in the chamber 1 h to render theinside of the food loading chambers 21 x, 21 y resistible against a highpressure during heating by high frequency application.

FIGS. 39A and 39B are diagrams showing a tenth modification of the foodloading container according to this invention. FIG. 39A is a plan view,and FIG. 39B is a cross-sectional side view. The food loading container1 i of this modification is of a type for maintaining a high-pressurizedstate in the food loading chamber to suppress expansion of theprepackaged food P during heating by high frequency application. Asshown in FIGS. 39A and 39B, the chamber 1 i essentially has a metallicupper-and-lower-part-dividable container main body 2 g of a circularshape in plan view, and a pair of opposing electrodes (lower electrode30 and upper electrode 40) equipped in the container main body 2 g.

The container main body 2 g includes a lower container main part 20 g ofa pan shape with a great depth and a cover 21 g of lid type that coversan upper peripheral end of the lower container main part 20 g. A lowerannular rib 271 projecting outward with a tapered portion as goingdownward is provided along an entire perimeter of the upper peripheralend of the lower container main part 20 g. Likewise, an upper annularrib 272 corresponding to the lower annular rib 271 with a taperedportion as going upward is provided along a peripheral end of the cover21 g. Mounting a pair of semi-circular clamp bands 273 formed with anengaging groove 273 a in an inner side thereof on a wedge-shape part incross section defined by joining the lower annular rib 271 and the upperannular rib 272 in mutually pressing contact state and fastening thesame with a bolt when the cover 21 g is placed over the lower containermain part 20 g securely sets the inside of the container main body 2 gin a sealably closed state.

An insertion hole is formed in a center of the cover 21 g to fittinglyinsert a fitting member 274 made of an insulating material. A conductivewire for supplying a high frequency power to the upper electrode 40 byway of the fitting member 274 is drawn into the container main body 2 g.

The container main body 2 g is constructed such that a lower hinge 31integrally mounted on the lower container main part 20 g and an upperhinge 41 integrally mounted on the cover 21 g are jointed pivotableabout respective horizontal axes relative to each other. Thereby, thecover 21 g is openably closed with respect to the lower container mainpart 20 g.

The lower electrode 30 is supported by a plurality of conductive barshape support members 293 provided upright on an inner bottom portion ofthe lower container main part 20 g. Likewise, the upper electrode 40 issupported by a plurality of bar shape support members 294 made of aninsulating material and provided upright from a ceiling of the cover 21g. A loading space for loading the prepackaged food P (Pa) is definedbetween the lower electrode 30 and the upper electrode 40. In thisembodiment, the loading space is secured by setting the planar size ofthe upper and lower electrode 30, 40 so as to place the prepackagedfoods P, Pa side by side.

A first auto coupler 275 for drawing a fluid into the container mainbody 2 g and a second auto coupler 276 for ejecting the fluid passingthrough the container main body 2 g are provided at a bottom portion ofthe lower container main part 20 g. Connecting a given tube to thecorresponding auto coupler 275 (276) according to needs switchinglydraws heated air, pressurized air, heated steam or cooling water intothe container main body 2 g by way of the first auto coupler 275 andejects the fluid once drawn into the container main body 2 g outtherefrom by way of the second auto coupler 276.

Mounting a sealing member 23 z which is rendered in planar contact withthe tray type prepackaged foods P between the lower electrode 30 and theupper electrode 40 enables dielectric heating of the prepackaged foods Pat 100° C. or higher without setting the inside of the container mainbody 2 g in a pressurized state by drawing pressurized air.

According to the food loading chamber 1 i of the tenth modification,since an entirety of the container main body 2 g except the fittingmember 274 is made of a metallic material, it can easily provide a foodloading container of a durable construction with less material cost,thus obtaining a desirable effect.

FIG. 40 is a plan view showing a fourteenth embodiment of the foodsterilizing apparatus according to this invention. As shown in thisdrawing, the food sterilizing apparatus 114 basically includes a foodprocessing table 900 of a square shape in plan view, and a U-shape subtable 901 in plan view extending by a certain length along left andright ends and a side end (lower part on the plane of FIG. 40) of thefood processing table 900. The food loading container 100 is processedfor sterilization due to dielectric heating while moving according to apredetermined order over the food processing table 900 and the sub table901.

The food processing table 900 has, in this embodiment, such a sizesufficient as to place 36 pieces of food loading containers 100 (6 percolumn×5 per row). Any type of food loading container as described inthe foregoing embodiments/modifications is applicable as the foodloading container 100. The sub table 901 includes a food receiving table902 provided in parallel with the side end of the food processing table900, a stand-by table 903 adjacent the table 900 at an upstream end(left end) in a container transport direction, and a food take-out table904 adjacent the table 900 at a downstream end (right end) in thecontainer transport direction.

Six pieces of food loading containers 100 that have moved onto the foodreceiving table 902 are transported to the stand-by table 903 by atransport roller 906 provided on the sub table 901 after loading of theprepackaged foods P (Pa) carried by a belt conveyor 905. These foodloading containers 100 are, after waiting for a predetermined time onthe stand-by table 903, fed onto the food processing table 900altogether as a set by a certain pushing means, and subjected to acertain sterilization while moved downstream, and carried onto the foodtake-out table 904.

Next, the set of containers 100 carried onto the food take-out table 904have their covers opened by a certain cover opening means, have theprepackaged foods P (Pa) loaded therein taken out by a certain take-outmeans, and are discharged out of the apparatus by a discharge conveyor907. After discharge of the prepackaged foods P (Pa), the set ofcontainers 100 are returned to the sub table 901 by the transport roller906 where another set of prepackaged foods P (Pa) are loaded.

In this way, a set of six containers 100 circulatively move over thefood receiving table 902, the stand-by table 903, the food processingtable 900, and the food take-out table 904. Thereby, the prepackagedfoods P (Pa) that have reached the apparatus 114 by the belt conveyor905 are loaded in the corresponding container 100, subjected to acertain sterilization, and then discharged as the sterilized prepackagedfoods P (Pa) by the discharge conveyor 907.

A preheating location R91, a dielectric heating location R92, and acooling location R93 are provided from upstream to downstream in thisorder on the food processing table 900. The prepackaged foods P (Pa) inthe container 100 is preheated by an external heat source at thepreheating location R91, sterilized due to dielectric heating whileapplied with a high frequency at the dielectric heating location R92,and cooled by an external cooling source such as cooling water at thecooling location R93.

Compact high frequency generators are mounted individually for each ofthe set of six containers 100 at the dielectric heating location R92 toperform dielectric heating onto the prepackaged foods P (Pa) loaded inthe containers 100 by the individually mounted high frequency generators907. The high frequency generators 907 are detached from the containers100 immediately before the containers 100 pass the dielectric heatinglocation R92 and detachably mounted to another set of containers 100that have entered the dielectric heating location R92.

Individually applying a high frequency to the set of containers 100 bythe compact high frequency generators 907 enables reliable dielectricheating with less heat variation among the prepackaged foods P (Pa) inthe food loading containers 100.

A high frequency generator 907 may be provided for all the food loadingcontainers 100 in advance, instead of detachably mounted to a set ofcontainers 100 that have reached the dielectric heating location R92 oneafter another. Alternatively, a high frequency power from one highfrequency generator 71 may be distributed to every single food loadingcontainer 100.

According to the food sterilizing apparatus 114 of the fourteenthembodiment, the prepackaged foods P (Pa) in the containers 100 providedin a densely arranged manner are applied with heat sterilization one setafter another successively. This arrangement reduces the installationarea for the apparatus, which is advantageous in effectively using afactory site.

FIG. 41 is a diagram showing an eleventh modification of the foodloading container according to this invention. The food loadingcontainer 1 j of this modification is, similar to the ninth modificationshown in FIGS. 38A and 38B, of a type where the tray type prepackagedfoods P are placed one over another in a container main body 2 h. Thecontainer main body 2 h includes a food loading chamber 21 z with such ashape that an intermediate portion thereof has a smaller size comparedwith upper and lower portions. The food loading chamber 21 z consists ofa lower food loading chamber 21 x′ and an upper food loading chamber 21y′. The other arrangement is substantially the same as the ninthmodification.

According to the food loading container 1 j of the eleventhmodification, each one of the prepackaged foods P can be loaded in lowerand upper parts of the food loading chamber 21 z (lowerfood loadingchamber 21 x′ and upperfood loading chamber 21 y′) without dividing thefood loading chamber 21 z into two parts.

FIG. 42 is a diagram showing a twelfth modification of the food loadingcontainer according to this invention. In the food loading container 1 kof this modification, two food loading chambers 21 j are defined side byside in a container main body 2 j. The inner shape of each of the foodloading chambers 21 j is set substantially the same as the outer shapeof the prepackaged food P.

According to the container 1 k of the twelfth modification, twoprepackaged foods P can be loaded side by side simultaneously in thecontainer main body 2 j.

As mentioned above in detail referring to each one of the embodimentsand modifications, the present invention is for sterilizing a sealablypacked prepackaged food due to dielectric heating by applying a highfrequency onto a food loading container loaded with the prepackagedfood. Fundamentally, adopted is a food loading container provided withat least one food loading chamber defined by a pair of opposingelectrodes and having such a shape as to load one prepackaged foodtherein. The food loading chamber has such an inner configuration as tosubstantially match the outer shape of the prepackaged food. Thisinvention also relates to various parts structures and devices that areused when actually performing dielectric heating onto the prepackagedfood loaded in the thus constructed food loading container.

The food loading container basically includes a pair of opposingelectrodes and an annular frame composed of an insulating materialinterposed between the electrode pair. However, as mentioned above indetail, there exist many types of electrodes such as a flat plate typeand the one formed with the recess as to match the shape of theprepackaged food. The parts structures involved in the arrangement ofthe food loading container include the one relating to the cylinderdevice for maintaining a closed state of the food loading chamber, thelocking mechanism for restricting opening of the food loading chamberonce locked, and the construction for supplying a heating medium to theopposing electrode pair. The devices involved in the arrangement of thefood loading container include the transport means such as the beltconveyor and the roller conveyor for circulatively transporting the foodloading containers, the prepackaged food loading means, the secondary(auxiliary) heating means to promote heating of the food loadingcontainer, the cooling means, and the food take-out means arranged alongthe transport path for the food loading containers.

Further, the arrangements on the structure and the facility that havebeen described in the other embodiments and modifications areapplicable, as far as not departing from the spirit of the invention, toany one of the food loading containers shown in the foregoingembodiments/modifications.

This invention is not limited to the embodiments and modificationsdescribed above and may contain the followings:

(1) In the first and second embodiments, the planar size of the opposingelectrode pair 20 is set substantially equal to that of the annularinsulator 23. In the fourth embodiment, the planar size of the opposingelectrode pair 20 a is set as to cover three annular insulators 23(transportable containers 23 a). Altematively, the size of the opposingelectrode pair 20 may be set as to cover two annular insulators 23 ormore than three.

(2) In the first to fourth embodiments, the lower pipe 430 is embeddedin the lower electrode 210, and the upper pipe 440 is embedded in theupper electrode 220. Alternatively, a horizontally extendingthrough-hole may be formed in the opposing electrode pair 20 to beconnected with the pipe.

(3) In the first to fourth embodiments, it is designed to selectivelysupply steam from the steam generator 410 and cooling water from thesupply source 420 into the space defined by the opposing electrode pair20 (20 a) by switching a supply timing. Supply of both steam and coolingwater into the space of the opposing electrode pair 20 (20 a) is notnecessarily required. Either one or none of the supply may be used.

(4) In the first to fourth embodiments, it is designed to draw a heatingmedium such as steam from the steam generator 410 and cooling water fromthe supply source 420 both into the upper electrode 220 (22 a) and lowerelectrode 210 (210 a, 210 b). Drawing may be conducted to either one ofthe upper and lower electrodes. Also, it may be preferable to form acommunication channel inside the sealing member 23 to supply a heatingmedium.

(5) In the first to fourth embodiments, provided is the second coolingstep X4 where the temperature of the prepackaged food P is lowered to anambient temperature, following the take-out step X3. Alternatively, thesecond cooling step X4 may be omitted, and the primary cooling step X23may be executed to lower the temperature of the prepackaged food P tothe ambient temperature. Also, it may be possible to cool theprepackaged food P to the ambient temperature by leaving it as it iswithout any process after the primary cooling step X23. In the case ofsolely depending on the primary cooling process, the temperature fallingcurve would follow the dotted line in FIG. 5B such that the temperaturefalling slope from the primary cooling process X23 follows thedotted-line state even at the region corresponding to the secondarycooling process X4.

(6) In the container 1 of the first modification, a locking means forlocking a closed state of the cover 4 is not provided. As an alteredform, similar to the container 1 a of the second embodiment, thecontainer 1 of the first embodiment may be provided with the lockingmeans 36. Thereby, even if the prepackaged food P is heated to 100° C.or higher, open-up of the cover 4 can be prevented. This arrangementeliminates the necessity of cooling the prepackaged food P whilepressingly holding the container 1 by the opposing electrode pair 72,which improves sterilizing efficiency of the apparatus 10 of the firstembodiment.

(7) In the apparatus 110 of the tenth embodiment, hot water from the hotwater source 61 of the preheating mechanism 6 is used as a heatingmedium for preheating the bottom plate 3 and the cover 4. Alternatively,heated steam or heated air (hot air) may be used in place of hot water.

(8) In the apparatus 111 of the eleventh embodiment, cooling of theprepackaged food Pa at the first and second cooling locations R14, R15by the upstream and downstream cooling mechanisms 8 a, 8 b is effectedby supplying cooling water from the water source 81 into the bottomplate 3 and the cover 4. Alternatively, drawing cooling water into thechamber 21 afor direct heat exchange of the heated prepackaged food Pawith the cooling water may cool the prepackaged food Pa.

(9) In the apparatus 111 of the eleventh embodiment, the bottom plate 3and the cover 4 are heated by heated steam from the boiler 801 of theexternal heating mechanism 80. Alternatively, hot water or heated airmay be supplied to the bottom plate 3 and the cover 4.

(10) In the apparatus 111 of the eleventh embodiment, heated air fromthe heater 601 of the pressurizing/preheating mechanism 60 is suppliedinto the food loading chamber 21 a of the container 1 a to preheat theprepackaged food Pa. In place of this arrangement, or in additionthereto, a heating medium may be supplied into the bottom plate 3 andthe cover 4 to preheat the prepackaged food Pa.

(11) In the apparatuses 110 (111) of the tenth (eleventh) embodiment,the container 1 (1 a) is circulatively moved by the conveyor belt 13(timing belt 130) with an upper and lower belt portion spaced away fromeach other. Alternatively, the container 1 (1 a) may be circulativelymoved over one horizontal plane.

(12) In the apparatus 110 (111) of the tenth (eleventh) embodiment, thefood take-out mechanism 9 is provided downstream of the coolingmechanism 8 (8 a, 8 b). The food take-out mechanism 9 has the coolingbath 91 for immersing the prepackaged food P (Pa) in water for cooling.As an altered arrangement, the cooling bath 91 may be omitted, and theprepackaged food P (Pa) may be cooled while transported along theconveyor belt or the like after taken out of the container 1 (1 a).

(13) In the container 1 f of the seventh modification, the casing 209and the cover 4 c may be set upside down with the bottom plate 3 dshielded. In this arrangement, the cover 4 c (now functioning as abottom plate) is normally set in an opened state, which eliminatesproviding a cover opening mechanism. In this case, it is required toprovide a cover closing mechanism. However, the structure of the coverclosing mechanism is generally simple compared with the structure of thecover opening mechanism because providing an intervening projection on atransport path for the container 1 f for causing the cover to closewhile passing the same would suffice the cover closing mechanism. Thisarrangement contributes to installation cost reduction.

Further, the container described in the foregoingembodiments/modifications may have the following features in the casethat the container is integrally provided with a construction thatenables keeping a closed state thereof:

(I) A prepackaged food loading container used in a prepackaged foodsterilizing apparatus provided with a high frequency generating sectionto supply a high frequency in order to sterilize a prepackaged food bydielectric heating has a holding mechanism for substantially holding aclosed state of the container loaded with the prepackaged food whileinterposed between a pair of opposing electrodes consisting of a firstelectrode and a second electrode for high frequency application. Theholding mechanism has an operating section for switching the state ofthe container between a closed state and an opened state.

(II) In the container set forth in (I), the holding mechanism has anengaging portion, and the operating section is operated to alter theposition of the engaging portion between an engaged position ofrendering the first and second electrodes in pressingly held state and arelease position of releasing the held state.

(III) In the container set forth in (I), an annular frame is interposedbetween the first and second electrodes, and a food loading chamber forloading the prepackaged food is defined in a space encased by theannular frame and the first and second electrodes.

(IV) In the container set forth in (III), the food loading chamber hassuch an inner shape as to substantially match the outer shape of theprepackaged food.

(V) In the container set forth in (III), the food loading chamber isconstructed to be sealably closed by pressing contact of the first andsecond electrodes with the annular frame.

(VI) In the container set forth in (I), the container has a main bodyfor enclosing the opposing electrode pair, and the holding mechanismsets the container main body to a sealably closed state.

EXPLOITATION IN INDUSTRY

According to the prepackaged food sterilizing apparatus and sterilizingmethod of this invention, the food loading chamber of the food loadingcontainer defined by the opposing electrode pair and the annular frameis adapted for loading one prepackaged food. Unlike the conventionalcase where a large number of prepackaged foods are loaded in a foodloading chamber of a large capacity to sterilize the foods by dielectricheating using a pair of opposing electrodes, which may result in adrawback that the heated temperature of the prepackaged foods variesdepending on the loaded position and the prepackaged foods withincomplete sterilization may be discharged, according to the inventiveapparatus, performing series-process such that a certain number ofprepackaged foods are loaded in the respective food loading chambers oneafter another and taken out therefrom successively after dielectricheating enables reliable sterilization onto the prepackaged foods.

Since the food loading chamber has such an inner shape as tosubstantially match the outer shape of the prepackaged food, expansionof the food due to dielectric heating is prevented by the inner wall ofthe food loading chamber which obstructs breaking of the bag/trayconstituting the container. This arrangement eliminates a necessity ofpressurizing the inside of the food loading chamber on a large scale toprevent burst-out of the food, and contributes to installation costreduction.

Furthermore, according to an aspect of this invention, a certain numberof containers are moved along the transport path as a set by thecontainer moving means, and the dielectric heating section forsterilizing the prepackaged food loaded in the container by dielectricheating is provided at an appropriate position on the transport path. Inthis arrangement, the plural prepackaged foods are moved along thetransport path one set after another to allow sterilization by thedielectric heating section successively. Compared to the conventionalarrangement in which a certain number of prepackaged foods are oncecarried near the dielectric heating section, and then dielectric heatingis applied to the foods one by one, this arrangement enables efficientheat sterilization.

In the above case, providing a prepackaged food loading mechanism forloading the prepackaged food in the container upstream of the dielectricheating section and a prepackaged food takeout mechanism for taking outthe sterilized prepackaged food from the food loading chamber downstreamenables automatic loading of the prepackaged food into the container fordielectric heating and automatic take-out of the sterilized food fromthe container without manpower. This arrangement contributes tooperation cost reduction.

What is claimed is:
 1. A prepackaged food sterilizing apparatus,comprising: a high frequency generating section for supplying a highfrequency voltage; a food loading container including a pair of opposingelectrodes having a first electrode and a second electrode,respectively, to which the high frequency is applied, said food loadingcontainer further including an annular frame interposed between the pairof first and second electrodes; a prepackaged food container forcontaining a food product therein, the food loading container includinga food loading chamber in which said prepackaged food container isreceivable, said food loading chamber and said prepackaged foodcontainer being configured to have respective shapes which aresubstantially complementary with one another such that said prepackagedfood container is conformably accommodated by an interior of said foodloading chamber over a substantial outer surface thereof when receivedin said food loading chamber at a time of sterilization of same, therebyproviding support against possible rupturing of said prepackaged foodcontainer caused by heat expansion; and a holding device operable tomaintain a position of the pair of opposing electrodes to retain a shapeof the food loading chamber which substantially conforms to acorresponding shape of the prepackaged food container.
 2. Theprepackaged food sterilizing apparatus according to claim 1, wherein:the first electrode and the second electrode are each formed with anopposing plane shaped into a flat surface parallel to each other; andthe annular frame has such an inner shape as to substantially match aside surface of the prepackaged food container.
 3. The prepackaged foodsterilizing apparatus according to claim 1, wherein: the first electrodeand the second electrode are formed with opposing planes, at least oneof the opposing planes of the first and second electrodes is formed witha recess of an inner shape substantially matching the outer shape of theprepackaged food container; and the annular frame is so shaped as tocome into contact with an outer surface of the prepackaged foodcontainer.
 4. The prepackaged food sterilizing apparatus according toclaim 1, wherein; the annular frame includes annular frame segmentsplaced one over another; and each of the annular frame segments has suchan inner shape substantially matching a side surface of the prepackagedfood container.
 5. The prepackaged food sterilizing apparatus accordingto claim 1, wherein the holding device includes a pressing device forpressing the first electrode against the second electrode.
 6. Theprepackaged food sterilizing apparatus according to claim 5, wherein thepressing device includes a cylinder device.
 7. The prepackaged foodsterilizing apparatus according to claim 1, wherein the holding deviceincludes an engaging device for restricting movement of the firstelectrode away from the second electrode.
 8. The prepackaged foodsterilizing apparatus according to claim 7, wherein the engaging deviceincludes an engaging portion and an operable tab to alter the positionof the engaging portion between an engaged position of rendering thefirst and second electrodes in a pressingly held state and a releaseposition of releasing the held state.
 9. The prepackaged foodsterilizing apparatus according to claim 7, wherein the engaging deviceincludes a band member for fastening the first and second electrodes.10. The prepackaged food sterilizing apparatus according to claim 1,further comprising a heater to promote heating of the prepackaged foodcontainer.
 11. The prepackaged food sterilizing apparatus according toclaim 1, further comprising a cooler for cooling the prepackaged foodcontainer after heated sterilization thereof.
 12. The prepackaged foodsterilizing apparatus according to claim 1, further comprising: atransport path for transporting the prepackaged food container; and ahigh frequency apply section provided on the way of the transport pathto apply a high frequency from the high frequency generating section tothe first and second electrodes with respect to at least one prepackagedfood container transported along the transport path.
 13. The prepackagedfood sterilizing apparatus according to claim 12, wherein the transportpath is constituted by a conveyor belt that circulatively moves betweena pair of rollers.
 14. The prepackaged food sterilizing apparatusaccording to claim 12, further comprising a prepackaged food loadingmechanism provided upstream of the transport path from the highfrequency apply section for loading the prepackaged food container intothe food loading container.
 15. The prepackaged food sterilizingapparatus according to claim 12, further comprising a prepackaged foodtakeout mechanism provided downstream of the transport path from thehigh frequency apply section for taking out the prepackaged foodcontainer from the food loading container.
 16. A prepackaged foodsterilizing apparatus, comprising: a high frequency generating sectionfor supplying a high frequency voltage; a food loading containerincluding a pair of opposing electrodes having a first electrode and asecond electrode, respectively, to which the high frequency is applied,said food loading container further including an annular frameinterposed between the pair of first and second electrodes; aprepackaged food container for containing a food product therein, thefood loading container including a food loading chamber in which saidprepackaged food container is receivable, said food loading chamber andsaid prepackaged food container being configured to have respectiveshapes which are substantially complementary with one another such thatsaid prepackaged food container is conformably accommodated by aninterior of said food loading chamber over a substantial outer surfacethereof when received in said food loading chamber at a time ofsterilization of same, thereby providing support against possiblerupturing of said prepackaged food container caused by heat expansion;and means for maintaining a position of the pair of opposing electrodesto retain a shape of the food loading chamber which substantiallyconforms to a corresponding shape of the prepackaged food container. 17.A method of sterilizing a container of prepackaged food, comprising:providing a food loading container which defines a food loading chamberpresenting an inner shape which is substantially equal to a shape of thecontainer of prepackaged food, the food loading chamber being defined bya pair of opposing electrodes and a frame member comprised of aninsulating material for holding the electrode pair in a spaced relation;loading the container of prepackaged food into the food loading chambersuch that said container is oriented therein in correspondingsubstantial conformance with the inner shape of the food loadingchamber; applying a high frequency from a high frequency generatingsection to a space defined by the opposing electrode pair while holdingthe container of prepackaged food in the food loading chamber tosterilize the container of prepackaged food by dielectric heating; andmaintaining a position of the pair of opposing electrodes to retain ashape of the food loading chamber defined at least in part by theopposing electrode pair which substantially conforms to a correspondingshape of the prepackaged food container at least during said step ofapplying.
 18. The method according to claim 17, further comprisingapplying a high frequency to the second electrodes with respect to thecontainer of prepackaged food while circulatively moving the containerof prepackaged food along a transport path.